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Manual Reference Pages  - Twig (3pm)

NAME

XML::Twig - A perl module for processing huge XML documents in tree mode.

CONTENTS

Synopsis
Description
XML::Twig 101
     Loading an XML document and processing it
     Processing an XML document chunk by chunk
     Processing just parts of an XML document
     Building an XML filter
     XML::Twig and various versions of Perl, XML::Parser and expat:
Simplifying XML processing
Classes
Methods
     XML::Twig
     XML::Twig::Elt
     cond
     XML::Twig::XPath
     XML::Twig::XPath::Elt
     XML::Twig::Entity_list
     XML::Twig::Entity
Examples
Notes
     Subclassing XML::Twig
     DTD Handling
     Flush
Bugs
Globals
Todo
Author
License
See Also
     Alternative Modules

SYNOPSIS

Note that this documentation is intended as a reference to the module.

Complete docs, including a tutorial, examples, an easier to use HTML version, a quick reference card and a FAQ are available at <http://www.xmltwig.com/xmltwig>

Small documents (loaded in memory as a tree):



  my $twig=XML::Twig->new();    # create the twig
  $twig->parsefile( doc.xml); # build it
  my_process( $twig);           # use twig methods to process it
  $twig->print;                 # output the twig



Huge documents (processed in combined stream/tree mode):



  # at most one div will be loaded in memory
  my $twig=XML::Twig->new(  
    twig_handlers =>
      { title   => sub { $_->set_tag( h2) }, # change title tags to h2
        para    => sub { $_->set_tag( p)  }, # change para to p
        hidden  => sub { $_->delete;       },  # remove hidden elements
        list    => \&my_list_process,          # process list elements
        div     => sub { $_[0]->flush;     },  # output and free memory
      },
    pretty_print => indented,                # output will be nicely formatted
    empty_tags   => html,                    # outputs <empty_tag />
                         );
    $twig->flush;                              # flush the end of the document



See XML::Twig 101 for other ways to use the module, as a filter for example.

DESCRIPTION

This module provides a way to process XML documents. It is build on top of CWXML::Parser.

The module offers a tree interface to the document, while allowing you to output the parts of it that have been completely processed.

It allows minimal resource (CPU and memory) usage by building the tree only for the parts of the documents that need actual processing, through the use of the CWtwig_roots and CWtwig_print_outside_roots options. The CWfinish and CWfinish_print methods also help to increase performances.

XML::Twig tries to make simple things easy so it tries its best to takes care of a lot of the (usually) annoying (but sometimes necessary) features that come with XML and XML::Parser.

XML::Twig 101

XML::Twig can be used either on small XML documents (that fit in memory) or on huge ones, by processing parts of the document and outputting or discarding them once they are processed.

    Loading an XML document and processing it



  my $t= XML::Twig->new();
  $t->parse( <d><title>title</title><para>p 1</para><para>p 2</para></d>);
  my $root= $t->root;
  $root->set_tag( html);              # change doc to html
  $title= $root->first_child( title); # get the title
  $title->set_tag( h1);               # turn it into h1
  my @para= $root->children( para);   # get the para children
  foreach my $para (@para)
    { $para->set_tag( p); }           # turn them into p
  $t->print;                            # output the document



Other useful methods include:

att: CW$elt->{att}->{foo} return the CWfoo attribute for an element,

set_att : CW$elt->set_att( foo => "bar") sets the CWfoo attribute to the CWbar value,

next_sibling: CW$elt->{next_sibling} return the next sibling in the document (in the example CW$title->{next_sibling} is the first CWpara, you can also (and actually should) use CW$elt->next_sibling( para) to get it

The document can also be transformed through the use of the cut, copy, paste and move methods: CW$title->cut; $title->paste( after => $p); for example

And much, much more, see XML::Twig::Elt.

    Processing an XML document chunk by chunk

One of the strengths of XML::Twig is that it let you work with files that do not fit in memory (BTW storing an XML document in memory as a tree is quite memory-expensive, the expansion factor being often around 10).

To do this you can define handlers, that will be called once a specific element has been completely parsed. In these handlers you can access the element and process it as you see fit, using the navigation and the cut-n-paste methods, plus lots of convenient ones like CWprefix . Once the element is completely processed you can then CWflush it, which will output it and free the memory. You can also CWpurge it if you don’t need to output it (if you are just extracting some data from the document for example). The handler will be called again once the next relevant element has been parsed.



  my $t= XML::Twig->new( twig_handlers =>
                          { section => \§ion,
                            para   => sub { $_->set_tag( p); }
                          },
                       );
  $t->parsefile( doc.xml);
  $t->flush; # dont forget to flush one last time in the end or anything
             # after the last </section> tag will not be output

  # the handler is called once a section is completely parsed, ie when
  # the end tag for section is found, it receives the twig itself and
  # the element (including all its sub-elements) as arguments
  sub section
    { my( $t, $section)= @_;      # arguments for all twig_handlers
      $section->set_tag( div);  # change the tag name.4, my favourite method...
      # lets use the attribute nb as a prefix to the title
      my $title= $section->first_child( title); # find the title
      my $nb= $title->{att}->{nb}; # get the attribute
      $title->prefix( "$nb - ");  # easy isnt it?
      $section->flush;            # outputs the section and frees memory
    }



There is of course more to it: you can trigger handlers on more elaborate conditions than just the name of the element, CWsection/title for example.



  my $t= XML::Twig->new( twig_handlers =>
                           { section/title => sub { $_->print } }
                       )
                  ->parsefile( doc.xml);



Here CWsub { $_->print } simply prints the current element (CW$_ is aliased to the element in the handler).

You can also trigger a handler on a test on an attribute:



  my $t= XML::Twig->new( twig_handlers =>
                      { section[@level="1"] => sub { $_->print } }
                       );
                  ->parsefile( doc.xml);



You can also use CWstart_tag_handlers to process an element as soon as the start tag is found. Besides CWprefix you can also use CWsuffix ,

    Processing just parts of an XML document

The twig_roots mode builds only the required sub-trees from the document Anything outside of the twig roots will just be ignored:



  my $t= XML::Twig->new(
       # the twig will include just the root and selected titles
           twig_roots   => { section/title => \&print_n_purge,
                             annex/title   => \&print_n_purge
           }
                      );
  $t->parsefile( doc.xml);

  sub print_n_purge
    { my( $t, $elt)= @_;
      print $elt->text;    # print the text (including sub-element texts)
      $t->purge;           # frees the memory
    }



You can use that mode when you want to process parts of a documents but are not interested in the rest and you don’t want to pay the price, either in time or memory, to build the tree for the it.

    Building an XML filter

You can combine the CWtwig_roots and the CWtwig_print_outside_roots options to build filters, which let you modify selected elements and will output the rest of the document as is.

This would convert prices in $ to prices in Euro in a document:



  my $t= XML::Twig->new(
           twig_roots   => { price => \&convert, },   # process prices
           twig_print_outside_roots => 1,               # print the rest
                      );
  $t->parsefile( doc.xml);

  sub convert
    { my( $t, $price)= @_;
      my $currency=  $price->{att}->{currency};          # get the currency
      if( $currency eq USD)
        { $usd_price= $price->text;                     # get the price
          # %rate is just a conversion table
          my $euro_price= $usd_price * $rate{usd2euro};
          $price->set_text( $euro_price);               # set the new price
          $price->set_att( currency => EUR);          # dont forget this!
        }
      $price->print;                                    # output the price
    }



    XML::Twig and various versions of Perl, XML::Parser and expat:

Before being uploaded to CPAN, XML::Twig 3.22 has been tested under the following environments:
linux-x86 perl 5.6.2, expat 1.95.8, XML::Parser 2.34 perl 5.8.0, expat 1.95.8, XML::Parser 2.34 perl 5.8.7, expat 1.95.8, XML::Parser2.34
Solaris perl 5.6.1, expat 1.95.2, XML::Parser 2.31
XML::Twig is a lot more sensitive to variations in versions of perl, XML::Parser and expat than to the OS, so this should cover some reasonable configurations.

The recommended configuration is perl 5.8.3+ (for good Unicode support), XML::Parser 2.31+ and expat 1.95.5+

See <http://testers.cpan.org/search?request=dist&dist=XML-Twig> for the CPAN testers reports on XML::Twig, which list all tested configurations.

An Atom feed of the CPAN Testers results is available at <http://xmltwig.com/rss/twig_testers.rss>

Finally:
XML::Twig does NOT work with expat 1.95.4
XML::Twig only works with XML::Parser 2.27 in perl 5.6.* Note that I can’t compile XML::Parser 2.27 anymore, so I can’t guarantee that it still works
XML::Parser 2.28 does not really work
When in doubt, upgrade expat, XML::Parser and Scalar::Util

Finally, for some optional features, XML::Twig depends on some additional modules. The complete list, which depends somewhat on the version of Perl that you are running, is given by running CWt/zz_dump_config.t

Simplifying XML processing

Whitespaces Whitespaces that look non-significant are discarded, this behaviour can be controlled using the CWkeep_spaces , CWkeep_spaces_in and CWdiscard_spaces_in options.
Encoding You can specify that you want the output in the same encoding as the input (provided you have valid XML, which means you have to specify the encoding either in the document or when you create the Twig object) using the CWkeep_encoding option

You can also use CWoutput_encoding to convert the internal UTF-8 format to the required encoding.

Comments and Processing Instructions (PI) Comments and PI’s can be hidden from the processing, but still appear in the output (they are carried by the real element closer to them)
Pretty Printing XML::Twig can output the document pretty printed so it is easier to read for us humans.
Surviving an untimely death XML parsers are supposed to react violently when fed improper XML. XML::Parser just dies.

XML::Twig provides the CWsafe_parse and the CWsafe_parsefile methods which wrap the parse in an eval and return either the parsed twig or 0 in case of failure.

Private attributes Attributes with a name starting with # (illegal in XML) will not be output, so you can safely use them to store temporary values during processing. Note that you can store anything in a private attribute, not just text, it’s just a regular Perl variable, so a reference to an object or a huge data structure is perfectly fine.

CLASSES

XML::Twig uses a very limited number of classes. The ones you are most likely to use are CWXML::Twig of course, which represents a complete XML document, including the document itself (the root of the document itself is CWroot), its handlers, its input or output filters... The other main class is CWXML::Twig::Elt, which models an XML element. Element here has a very wide definition: it can be a regular element, or but also text, with an element CWtag of CW#PCDATA (or CW#CDATA), an entity (tag is CW#ENT), a Processing Instruction (CW#PI), a comment (CW#COMMENT).

Those are the 2 commonly used classes.

You might want to look the CWelt_class option if you want to subclass CWXML::Twig::Elt.

Attributes are just attached to their parent element, they are not objects per se. (Please use the provided methods CWatt and CWset_att to access them, if you access them as a hash, then your code becomes implementaion dependent and might break in the future).

Other classes that are seldom used are CWXML::Twig::Entity_list and CWXML::Twig::Entity.

If you use CWXML::Twig::XPath instead of CWXML::Twig, elements are then created as CWXML::Twig::XPath::Elt

METHODS

    XML::Twig

A twig is a subclass of XML::Parser, so all XML::Parser methods can be called on a twig object, including parse and parsefile. CWsetHandlers on the other hand cannot be used, see CWBUGS
new This is a class method, the constructor for XML::Twig. Options are passed as keyword value pairs. Recognized options are the same as XML::Parser, plus some XML::Twig specifics.

New Options:
twig_handlers This argument consists of a hash CW{ expression = \&handler}> where expression is a an XPath-like expression (+ some others).

XPath expressions are limited to using the child and descendant axis (indeed you can’t specify an axis), and predicates cannot be nested. You can use the CWstring, or CWstring(<tag>) function (except in CWtwig_roots triggers).

Additionally you can use regexps (/ delimited) to match attribute and string values.

Examples:



  foo
  foo/bar
  foo//bar
  /foo/bar
  /foo//bar
  /foo/bar[@att1 = "val1" and @att2 = "val2"]/baz[@a >= 1]
  foo[string()=~ /^duh!+/]
  /foo[string(bar)=~ /\d+/]/baz[@att != 3]



#CDATA can be used to call a handler for a CDATA. #COMMENT can be used to call a handler for comments

Some additional (non-XPath) expressions are also provided for convenience:
processing instructions CW? or CW#PI triggers the handler for any processing instruction, and CW?<target> or CW#PI <target> triggers a handler for processing instruction with the given target( ex: CW#PI xml-stylesheet).
level(<level>) Triggers the handler on any element at that level in the tree (root is level 1)
_all_ Triggers the handler for all elements in the tree
_default_ Triggers the handler for each element that does NOT have any other handler.

Expressions are evaluated against the input document. Which means that even if you have changed the tag of an element (changing the tag of a parent element from a handler for example) the change will not impact the expression evaluation. There is an exception to this: private attributes (which name start with a ’#’, and can only be created during the parsing, as they are not valid XML) are checked against the current twig.

Handlers are triggered in fixed order, sorted by their type (xpath expressions first, then regexps, then level), then by whether they specify a full path (starting at the root element) or not, then by by number of steps in the expression , then number of predicates, then number of tests in predicates. Handlers where the last step does not specify a step (CWfoo/bar/*) are triggered after other XPath handlers. Finally CW_all_ handlers are triggered last.

Important: once a handler has been triggered if it returns 0 then no other handler is called, except a CW_all_ handler which will be called anyway.

If a handler returns a true value and other handlers apply, then the next applicable handler will be called. Repeat, rinse, lather..; The exception to that rule is when the CWdo_not_chain_handlers option is set, in which case only the first handler will be called.

Note that it might be a good idea to explicitly return a short true value (like 1) from handlers: this ensures that other applicable handlers are called even if the last statement for the handler happens to evaluate to false. This might also speedup the code by avoiding the result of the last statement of the code to be copied and passed to the code managing handlers. It can really pay to have 1 instead of a long string returned.

When an element is CLOSED the corresponding handler is called, with 2 arguments: the twig and the CWElement . The twig includes the document tree that has been built so far, the element is the complete sub-tree for the element. This means that handlers for inner elements are called before handlers for outer elements.

CW$_ is also set to the element, so it is easy to write inline handlers like



  para => sub { $_->set_tag( p); }



Text is stored in elements whose tag is #PCDATA (due to mixed content, text and sub-element in an element there is no way to store the text as just an attribute of the enclosing element).

Warning: if you have used purge or flush on the twig the element might not be complete, some of its children might have been entirely flushed or purged, and the start tag might even have been printed (by CWflush) already, so changing its tag might not give the expected result.

twig_roots This argument let’s you build the tree only for those elements you are interested in.



  Example: my $t= XML::Twig->new( twig_roots => { title => 1, subtitle => 1});
           $t->parsefile( file);
           my $t= XML::Twig->new( twig_roots => { section/title => 1});
           $t->parsefile( file);



return a twig containing a document including only CWtitle and CWsubtitle elements, as children of the root element.

You can use generic_attribute_condition, attribute_condition, full_path, partial_path, tag, tag_regexp, _default_ and _all_ to trigger the building of the twig. string_condition and regexp_condition cannot be used as the content of the element, and the string, have not yet been parsed when the condition is checked.

WARNING: path are checked for the document. Even if the CWtwig_roots option is used they will be checked against the full document tree, not the virtual tree created by XML::Twig

WARNING: twig_roots elements should NOT be nested, that would hopelessly confuse XML::Twig ;--(

Note: you can set handlers (twig_handlers) using twig_roots
Example: my CW$t= XML::Twig->new( twig_roots =>
{ title => sub { CW$_{1]->print;},
subtitle => \&process_subtitle
}
);
CW$t->parsefile( file);

twig_print_outside_roots To be used in conjunction with the CWtwig_roots argument. When set to a true value this will print the document outside of the CWtwig_roots elements.



 Example: my $t= XML::Twig->new( twig_roots => { title => \&number_title },
                                twig_print_outside_roots => 1,
                               );
           $t->parsefile( file);
           { my $nb;
           sub number_title
             { my( $twig, $title);
               $nb++;
               $title->prefix( "$nb "; }
               $title->print;
             }
           }



This example prints the document outside of the title element, calls CWnumber_title for each CWtitle element, prints it, and then resumes printing the document. The twig is built only for the CWtitle elements.

If the value is a reference to a file handle then the document outside the CWtwig_roots elements will be output to this file handle:



  open( OUT, ">out_file") or die "cannot open out file out_file:$!";
  my $t= XML::Twig->new( twig_roots => { title => \&number_title },
                         # default output to OUT
                         twig_print_outside_roots => \*OUT,
                       );

         { my $nb;
           sub number_title
             { my( $twig, $title);
               $nb++;
               $title->prefix( "$nb "; }
               $title->print( \*OUT);    # you have to print to \*OUT here
             }
           }



start_tag_handlers A hash CW{ expression = \&handler}>. Sets element handlers that are called when the element is open (at the end of the XML::Parser CWStart handler). The handlers are called with 2 params: the twig and the element. The element is empty at that point, its attributes are created though.

You can use generic_attribute_condition, attribute_condition, full_path, partial_path, tag, tag_regexp, _default_ and _all_ to trigger the handler.

string_condition and regexp_condition cannot be used as the content of the element, and the string, have not yet been parsed when the condition is checked.

The main uses for those handlers are to change the tag name (you might have to do it as soon as you find the open tag if you plan to CWflush the twig at some point in the element, and to create temporary attributes that will be used when processing sub-element with CWtwig_hanlders.

You should also use it to change tags if you use CWflush. If you change the tag in a regular CWtwig_handler then the start tag might already have been flushed.

Note: CWstart_tag handlers can be called outside of CWtwig_roots if this argument is used, in this case handlers are called with the following arguments: CW$t (the twig), CW$tag (the tag of the element) and CW%att (a hash of the attributes of the element).

If the CWtwig_print_outside_roots argument is also used, if the last handler called returns a CWtrue value, then the the start tag will be output as it appeared in the original document, if the handler returns a a CWfalse value then the start tag will not be printed (so you can print a modified string yourself for example).

Note that you can use the ignore method in CWstart_tag_handlers (and only there).

end_tag_handlers A hash CW{ expression = \&handler}>. Sets element handlers that are called when the element is closed (at the end of the XML::Parser CWEnd handler). The handlers are called with 2 params: the twig and the tag of the element.

twig_handlers are called when an element is completely parsed, so why have this redundant option? There is only one use for CWend_tag_handlers: when using the CWtwig_roots option, to trigger a handler for an element outside the roots. It is for example very useful to number titles in a document using nested sections:



  my @no= (0);
  my $no;
  my $t= XML::Twig->new(
          start_tag_handlers =>
           { section => sub { $no[$#no]++; $no= join ., @no; push @no, 0; } },
          twig_roots         =>
           { title   => sub { $_[1]->prefix( $no); $_[1]->print; } },
          end_tag_handlers   => { section => sub { pop @no;  } },
          twig_print_outside_roots => 1
                      );
   $t->parsefile( $file);



Using the CWend_tag_handlers argument without CWtwig_roots will result in an error.

do_not_chain_handlers If this option is set to a true value, then only one handler will be called for each element, even if several satisfy the condition

Note that the CW_all_ handler will still be called regardless

ignore_elts This option lets you ignore elements when building the twig. This is useful in cases where you cannot use CWtwig_roots to ignore elements, for example if the element to ignore is a sibling of elements you are interested in.

Example:



  my $twig= XML::Twig->new( ignore_elts => { elt => 1 });
  $twig->parsefile( doc.xml);



This will build the complete twig for the document, except that all CWelt elements (and their children) will be left out.

char_handler A reference to a subroutine that will be called every time CWPCDATA is found.

The subroutine receives the string as argument, and returns the modified string:



  # we want all strings in upper case
  sub my_char_handler
    { my( $text)= @_;
      $text= uc( $text);
      return $text;
    }



elt_class The name of a class used to store elements. this class should inherit from CWXML::Twig::Elt (and by default it is CWXML::Twig::Elt). This option is used to subclass the element class and extend it with new methods.

This option is needed because during the parsing of the XML, elements are created by CWXML::Twig, without any control from the user code.

keep_atts_order Setting this option to a true value causes the attribute hash to be tied to a CWTie::IxHash object. This means that CWTie::IxHash needs to be installed for this option to be available. It also means that the hash keeps its order, so you will get the attributes in order. This allows outputting the attributes in the same order as they were in the original document.
keep_encoding This is a (slightly?) evil option: if the XML document is not UTF-8 encoded and you want to keep it that way, then setting keep_encoding will use theCWExpat original_string method for character, thus keeping the original encoding, as well as the original entities in the strings.

See the CWt/test6.t test file to see what results you can expect from the various encoding options.

WARNING: if the original encoding is multi-byte then attribute parsing will be EXTREMELY unsafe under any Perl before 5.6, as it uses regular expressions which do not deal properly with multi-byte characters. You can specify an alternate function to parse the start tags with the CWparse_start_tag option (see below)

WARNING: this option is NOT used when parsing with the non-blocking parser (CWparse_start, CWparse_more, parse_done methods) which you probably should not use with XML::Twig anyway as they are totally untested!

output_encoding This option generates an output_filter using CWEncode, CWText::Iconv or CWUnicode::Map8 and CWUnicode::Strings, and sets the encoding in the XML declaration. This is the easiest way to deal with encodings, if you need more sophisticated features, look at CWoutput_filter below
output_filter This option is used to convert the character encoding of the output document. It is passed either a string corresponding to a predefined filter or a subroutine reference. The filter will be called every time a document or element is processed by the print functions (CWprint, CWsprint, CWflush).

Pre-defined filters:
latin1 uses either CWEncode, CWText::Iconv or CWUnicode::Map8 and CWUnicode::String or a regexp (which works only with XML::Parser 2.27), in this order, to convert all characters to ISO-8859-1 (aka latin1)
html does the same conversion as CWlatin1, plus encodes entities using CWHTML::Entities (oddly enough you will need to have HTML::Entities installed for it to be available). This should only be used if the tags and attribute names themselves are in US-ASCII, or they will be converted and the output will not be valid XML any more
safe converts the output to ASCII (US) only plus character entities (CW&#nnn;) this should be used only if the tags and attribute names themselves are in US-ASCII, or they will be converted and the output will not be valid XML any more
safe_hex same as CWsafe except that the character entities are in hexa (CW&#xnnn;)
encode_convert ($encoding) Return a subref that can be used to convert utf8 strings to CW$encoding). Uses CWEncode.



   my $conv = XML::Twig::encode_convert( latin1);
   my $t = XML::Twig->new(output_filter => $conv);



iconv_convert ($encoding) this function is used to create a filter subroutine that will be used to convert the characters to the target encoding using CWText::Iconv (which needs to be installed, look at the documentation for the module and for the CWiconv library to find out which encodings are available on your system)



   my $conv = XML::Twig::iconv_convert( latin1);
   my $t = XML::Twig->new(output_filter => $conv);



unicode_convert ($encoding) this function is used to create a filter subroutine that will be used to convert the characters to the target encoding using CWUnicode::Strings and CWUnicode::Map8 (which need to be installed, look at the documentation for the modules to find out which encodings are available on your system)



   my $conv = XML::Twig::unicode_convert( latin1);
   my $t = XML::Twig->new(output_filter => $conv);



The CWtext and CWatt methods do not use the filter, so their result are always in unicode.

Those predeclared filters are based on subroutines that can be used by themselves (as CWXML::Twig::foo).
html_encode ($string) Use CWHTML::Entities to encode a utf8 string
safe_encode ($string) Use either a regexp (perl < 5.8) or CWEncode to encode non-ascii characters in the string in CW&#<nnnn>; format
safe_encode_hex ($string) Use either a regexp (perl < 5.8) or CWEncode to encode non-ascii characters in the string in CW&#x<nnnn>; format
regexp2latin1 ($string) Use a regexp to encode a utf8 string into latin 1 (ISO-8859-1). Does not work with Perl 5.8.0!

output_text_filter same as output_filter, except it doesn’t apply to the brackets and quotes around attribute values. This is useful for all filters that could change the tagging, basically anything that does not just change the encoding of the output. CWhtml, CWsafe and CWsafe_hex are better used with this option.
input_filter This option is similar to CWoutput_filter except the filter is applied to the characters before they are stored in the twig, at parsing time.
remove_cdata Setting this option to a true value will force the twig to output CDATA sections as regular (escaped) PCDATA
parse_start_tag If you use the CWkeep_encoding option then this option can be used to replace the default parsing function. You should provide a coderef (a reference to a subroutine) as the argument, this subroutine takes the original tag (given by XML::Parser::Expat CWoriginal_string() method) and returns a tag and the attributes in a hash (or in a list attribute_name/attribute value).
expand_external_ents When this option is used external entities (that are defined) are expanded when the document is output using print functions such as CWprint , CWsprint , CWflush and CWxml_string . Note that in the twig the entity will be stored as an element with a tag ’CW#ENT’, the entity will not be expanded there, so you might want to process the entities before outputting it.

If an external entity is not available, then the parse will fail.

A special case is when the value of this option is -1. In that case a missing entity will not cause the parser to die, but its CWname, CWsysid and CWpubid will be stored in the twig as CW$twig->{twig_missing_system_entities} (a reference to an array of hashes { name => <name>, sysid => <sysid>, pubid => <pubid> }). Yes, this is a bit of a hack, but it’s useful in some cases.

load_DTD If this argument is set to a true value, CWparse or CWparsefile on the twig will load the DTD information. This information can then be accessed through the twig, in a CWDTD_handler for example. This will load even an external DTD.

Default and fixed values for attributes will also be filled, based on the DTD.

Note that to do this the module will generate a temporary file in the current directory. If this is a problem let me know and I will add an option to specify an alternate directory.

See DTD Handling for more information

DTD_handler Set a handler that will be called once the doctype (and the DTD) have been loaded, with 2 arguments, the twig and the DTD.
no_prolog Does not output a prolog (XML declaration and DTD)
id This optional argument gives the name of an attribute that can be used as an ID in the document. Elements whose ID is known can be accessed through the elt_id method. id defaults to ’id’. See CWBUGS
discard_spaces If this optional argument is set to a true value then spaces are discarded when they look non-significant: strings containing only spaces are discarded. This argument is set to true by default.
keep_spaces If this optional argument is set to a true value then all spaces in the document are kept, and stored as CWPCDATA.

Warning: adding this option can result in changes in the twig generated: space that was previously discarded might end up in a new text element. see the difference by calling the following code with 0 and 1 as arguments:



  perl -MXML::Twig -eprint XML::Twig->new( keep_spaces => shift)->parse( "<d> \n<e/></d>")->_dump



CWkeep_spaces and CWdiscard_spaces cannot be both set.

discard_spaces_in This argument sets CWkeep_spaces to true but will cause the twig builder to discard spaces in the elements listed.

The syntax for using this argument is:



  XML::Twig->new( discard_spaces_in => [ elt1, elt2]);



keep_spaces_in This argument sets CWdiscard_spaces to true but will cause the twig builder to keep spaces in the elements listed.

The syntax for using this argument is:



  XML::Twig->new( keep_spaces_in => [ elt1, elt2]);



Warning: adding this option can result in changes in the twig generated: space that was previously discarded might end up in a new text element.

pretty_print Set the pretty print method, amongst ’CWnone’ (default), ’CWnsgmls’, ’CWnice’, ’CWindented’, ’CWindented_c’, ’CWindented_a’, ’CWindented_close_tag’, ’CWcvs’, ’CWwrapped’, ’CWrecord’ and ’CWrecord_c

pretty_print formats:
none The document is output as one ling string, with no line breaks except those found within text elements
nsgmls Line breaks are inserted in safe places: that is within tags, between a tag and an attribute, between attributes and before the > at the end of a tag.

This is quite ugly but better than CWnone, and it is very safe, the document will still be valid (conforming to its DTD).

This is how the SGML parser CWsgmls splits documents, hence the name.

nice This option inserts line breaks before any tag that does not contain text (so element with textual content are not broken as the \n is the significant).

WARNING: this option leaves the document well-formed but might make it invalid (not conformant to its DTD). If you have elements declared as



  <!ELEMENT foo (#PCDATA|bar)>



then a CWfoo element including a CWbar one will be printed as



  <foo>
  <bar>bar is just pcdata</bar>
  </foo>



This is invalid, as the parser will take the line break after the CWfoo tag as a sign that the element contains PCDATA, it will then die when it finds the CWbar tag. This may or may not be important for you, but be aware of it!

indented Same as CWnice (and with the same warning) but indents elements according to their level
indented_c Same as CWindented but a little more compact: the closing tags are on the same line as the preceding text
indented_close_tag Same as CWindented except that the closing tag is also indented, to line up with the tags within the element
idented_a This formats XML files in a line-oriented version control friendly way. The format is described in <http://tinyurl.com/2kwscq> (that’s an Oracle document with an insanely long URL).

Note that to be totaly conformant to the spec, the order of attributes should not be changed, so if they are not already in alphabetical order you will need to use the CWkeep_atts_order option.

cvs Same as CWidented_a.
wrapped Same as CWindented_c but lines are wrapped using Text::Wrap::wrap. The default length for lines is the default for CW$Text::Wrap::columns, and can be changed by changing that variable.
record This is a record-oriented pretty print, that display data in records, one field per line (which looks a LOT like CWindented)
record_c Stands for record compact, one record per line

empty_tags Set the empty tag display style (’CWnormal’, ’CWhtml’ or ’CWexpand’).

CWnormal outputs an empty tag ’CW<tag/>’, CWhtml adds a space ’CW<tag />’ for elements that can be empty in XHTML and CWexpand outputs ’CW<tag></tag>

quote Set the quote character for attributes (’CWsingle’ or ’CWdouble’).
escape_gt By default XML::Twig does not escape the character > in its output, as it is not mandated by the XML spec. With this option on, > will be replaced by CW>
comments Set the way comments are processed: ’CWdrop’ (default), ’CWkeep’ or ’CWprocess

Comments processing options:
drop drops the comments, they are not read, nor printed to the output
keep comments are loaded and will appear on the output, they are not accessible within the twig and will not interfere with processing though

Note: comments in the middle of a text element such as



  <p>text <!-- comment --> more text --></p>



are kept at their original position in the text. Using print methods like CWprint or CWsprint will return the comments in the text. Using CWtext or CWfield on the other hand will not.

Any use of CWset_pcdata on the CW#PCDATA element (directly or through other methods like CWset_content) will delete the comment(s).

process comments are loaded in the twig and will be treated as regular elements (their CWtag is CW#COMMENT) this can interfere with processing if you expect CW$elt->{first_child} to be an element but find a comment there. Validation will not protect you from this as comments can happen anywhere. You can use CW$elt->first_child( tag) (which is a good habit anyway) to get where you want.

Consider using CWprocess if you are outputting SAX events from XML::Twig.

pi Set the way processing instructions are processed: ’CWdrop’, ’CWkeep’ (default) or ’CWprocess

Note that you can also set PI handlers in the CWtwig_handlers option:



  ?       => \&handler
  ?target => \&handler 2



The handlers will be called with 2 parameters, the twig and the PI element if CWpi is set to CWprocess, and with 3, the twig, the target and the data if CWpi is set to CWkeep. Of course they will not be called if CWpi is set to CWdrop.

If CWpi is set to CWkeep the handler should return a string that will be used as-is as the PI text (it should look like "CW <?target data? >" or ’’ if you want to remove the PI),

Only one handler will be called, CW?target or CW? if no specific handler for that target is available.

map_xmlns This option is passed a hashref that maps uri’s to prefixes. The prefixes in the document will be replaced by the ones in the map. The mapped prefixes can (actually have to) be used to trigger handlers, navigate or query the document.

Here is an example:



  my $t= XML::Twig->new( map_xmlns => {http://www.w3.org/2000/svg => "svg"},
                         twig_handlers =>
                           { svg:circle => sub { $_->set_att( r => 20) } },
                         pretty_print => indented,
                       )
                  ->parse( <doc xmlns:gr="http://www.w3.org/2000/svg">
                              <gr:circle cx="10" cy="90" r="10"/>
                           </doc>
                         )
                  ->print;



This will output:



  <doc xmlns:svg="http://www.w3.org/2000/svg">
     <svg:circle cx="10" cy="90" r="20"/>
  </doc>



keep_original_prefix When used with CWmap_xmlns this option will make CWXML::Twig use the original namespace prefixes when outputting a document. The mapped prefix will still be used for triggering handlers and in navigation and query methods.



  my $t= XML::Twig->new( map_xmlns => {http://www.w3.org/2000/svg => "svg"},
                         twig_handlers =>
                           { svg:circle => sub { $_->set_att( r => 20) } },
                         keep_original_prefix => 1,
                         pretty_print => indented,
                       )
                  ->parse( <doc xmlns:gr="http://www.w3.org/2000/svg">
                              <gr:circle cx="10" cy="90" r="10"/>
                           </doc>
                         )
                  ->print;



This will output:



  <doc xmlns:gr="http://www.w3.org/2000/svg">
     <gr:circle cx="10" cy="90" r="20"/>
  </doc>



index ($arrayref or CW$hashref) This option creates lists of specific elements during the parsing of the XML. It takes a reference to either a list of triggering expressions or to a hash name => expression, and for each one generates the list of elements that match the expression. The list can be accessed through the CWindex method.

example:



  # using an array ref
  my $t= XML::Twig->new( index => [ div, table ])
                  ->parsefile( "foo.xml);
  my $divs= $t->index( div);
  my $first_div= $divs->[0];
  my $last_table= $t->index( table => -1);

  # using a hashref to name the indexes
  my $t= XML::Twig->new( index => { email => a[@href=~/^\s*mailto:/])
                  ->parsefile( "foo.xml);
  my $last_emails= $t->index( email => -1);



Note that the index is not maintained after the parsing. If elements are deleted, renamed or otherwise hurt during processing, the index is NOT updated.

Note: I _HATE_ the Java-like name of arguments used by most XML modules. So in pure TIMTOWTDI fashion all arguments can be written either as CWUglyJavaLikeName or as CWreadable_perl_name: CWtwig_print_outside_roots or CWTwigPrintOutsideRoots (or even CWtwigPrintOutsideRoots {shudder}). XML::Twig normalizes them before processing them.

parse ( CW$source) The CW$source parameter should either be a string containing the whole XML document, or it should be an open CWIO::Handle. Constructor options to CWXML::Parser::Expat given as keyword-value pairs may follow theCW$source parameter. These override, for this call, any options or attributes passed through from the XML::Parser instance.

A die call is thrown if a parse error occurs. Otherwise it will return the twig built by the parse. Use CWsafe_parse if you want the parsing to return even when an error occurs.

If this method is called as a class method (CWXML::Twig->parse( $some_xml_or_html)) then an XML::Twig object is created, using the parameters except the last one (eg CWXML::Twig->parse( pretty_print => indented, $some_xml_or_html)) and CWxparse is called on it.

parsestring This is just an alias for CWparse for backwards compatibility.
parsefile (FILE [, OPT => OPT_VALUE [...]]) Open CWFILE for reading, then call CWparse with the open handle. The file is closed no matter how CWparse returns.

A CWdie call is thrown if a parse error occurs. Otherwise it will return the twig built by the parse. Use CWsafe_parsefile if you want the parsing to return even when an error occurs.

parsefile_inplace ( CW$file, CW$optional_extension) Parse and update a file in place. It does this by creating a temp file, selecting it as the default for print() statements (and methods), then parsing the input file. If the parsing is successful, then the temp file is moved to replace the input file.

If an extension is given then the original file is backed-up (the rules for the extension are the same as the rule for the -i option in perl).

parsefile_html_inplace ( CW$file, CW$optional_extension) Same as parsefile_inplace, except that it parses HTML instead of XML
parseurl ($url CW$optional_user_agent) Gets the data from CW$url and parse it. The data is piped to the parser in chunks the size of the XML::Parser::Expat buffer, so memory consumption and hopefully speed are optimal.

For most (read small) XML it is probably as efficient (and easier to debug) to just CWget the XML file and then parse it as a string.



  use XML::Twig;
  use LWP::Simple;
  my $twig= XML::Twig->new();
  $twig->parse( LWP::Simple::get( $URL ));



or



  use XML::Twig;
  my $twig= XML::Twig->nparse( $URL);



If the CW$optional_user_agent argument is used then it is used, otherwise a new one is created.

safe_parse ( SOURCE [, OPT => OPT_VALUE [...]]) This method is similar to CWparse except that it wraps the parsing in an CWeval block. It returns the twig on success and 0 on failure (the twig object also contains the parsed twig). CW$@ contains the error message on failure.

Note that the parsing still stops as soon as an error is detected, there is no way to keep going after an error.

safe_parsefile (FILE [, OPT => OPT_VALUE [...]]) This method is similar to CWparsefile except that it wraps the parsing in an CWeval block. It returns the twig on success and 0 on failure (the twig object also contains the parsed twig) . CW$@ contains the error message on failure

Note that the parsing still stops as soon as an error is detected, there is no way to keep going after an error.

safe_parseurl ($url CW$optional_user_agent) Same as CWparseurl except that it wraps the parsing in an CWeval block. It returns the twig on success and 0 on failure (the twig object also contains the parsed twig) . CW$@ contains the error message on failure
parse_html ($string_or_fh) parse an HTML string or file handle (by converting it to XML using HTML::TreeBuilder, which needs to be available).

This works nicely, but some information gets lost in the process: newlines are removed, and (at least on the version I use), comments get get an extra CDATA section inside ( <!-- foo --> becomes <!-- <![CDATA[ foo ]]> -->

parsefile_html parse an HTML file (by converting it to XML using HTML::TreeBuilder, which needs to be available). The file is loaded completely in memory and converted to XML before being parsed.

Alpha: implementation, and thus generated XML could change.

safe_parseurl_html ($url CW$optional_user_agent) Same as CWparseurl_html> except that it wraps the parsing in an CWeval block. It returns the twig on success and 0 on failure (the twig object also contains the parsed twig) . CW$@ contains the error message on failure
safe_parsefile_html ($file CW$optional_user_agent) Same as CWparsefile_html> except that it wraps the parsing in an CWeval block. It returns the twig on success and 0 on failure (the twig object also contains the parsed twig) . CW$@ contains the error message on failure
safe_parse_html ($string_or_fh) Same as CWparse_html except that it wraps the parsing in an CWeval block. It returns the twig on success and 0 on failure (the twig object also contains the parsed twig) . CW$@ contains the error message on failure
xparse ($thing_to_parse) parse the CW$thing_to_parse, whether it is a filehandle, a string, an HTML file, an HTML URL, an URL or a file.

Note that this is mostly a convenience method for one-off scripts. For example files that end in ’.htm’ or ’.html’ are parsed first as XML, and if this fails as HTML. This is certainly not the most efficient way to do this in general.

nparse ($optional_twig_options, CW$thing_to_parse) create a twig with the CW$optional_options, and parse the CW$thing_to_parse, whether it is a filehandle, a string, an HTML file, an HTML URL, an URL or a file.

Examples:



   XML::Twig->nparse( "file.xml");
   XML::Twig->nparse( error_context => 1, "file://file.xml");



nparse_pp ($optional_twig_options, CW$thing_to_parse) same as CWnparse but also sets the CWpretty_print option to CWindented.
nparse_e ($optional_twig_options, CW$thing_to_parse) same as CWnparse but also sets the CWerror_context option to 1.
nparse_ppe ($optional_twig_options, CW$thing_to_parse) same as CWnparse but also sets the CWpretty_print option to CWindented and the CWerror_context option to 1.
parser This method returns the CWexpat object (actually the XML::Parser::Expat object) used during parsing. It is useful for example to call XML::Parser::Expat methods on it. To get the line of a tag for example use CW$t->parser->current_line.
setTwigHandlers ($handlers) Set the twig_handlers. CW$handlers is a reference to a hash similar to the one in the CWtwig_handlers option of new. All previous handlers are unset. The method returns the reference to the previous handlers.
setTwigHandler ($exp CW$handler) Set a single twig_handler for elements matching CW$exp. CW$handler is a reference to a subroutine. If the handler was previously set then the reference to the previous handler is returned.
setStartTagHandlers ($handlers) Set the start_tag handlers. CW$handlers is a reference to a hash similar to the one in the CWstart_tag_handlers option of new. All previous handlers are unset. The method returns the reference to the previous handlers.
setStartTagHandler ($exp CW$handler) Set a single start_tag handlers for elements matching CW$exp. CW$handler is a reference to a subroutine. If the handler was previously set then the reference to the previous handler is returned.
setEndTagHandlers ($handlers) Set the end_tag handlers. CW$handlers is a reference to a hash similar to the one in the CWend_tag_handlers option of new. All previous handlers are unset. The method returns the reference to the previous handlers.
setEndTagHandler ($exp CW$handler) Set a single end_tag handlers for elements matching CW$exp. CW$handler is a reference to a subroutine. If the handler was previously set then the reference to the previous handler is returned.
setTwigRoots ($handlers) Same as using the CWtwig_roots option when creating the twig
setCharHandler ($exp CW$handler) Set a CWchar_handler
setIgnoreEltsHandler ($exp) Set a CWignore_elt handler (elements that match CW$exp will be ignored
setIgnoreEltsHandlers ($exp) Set all CWignore_elt handlers (previous handlers are replaced)
dtd Return the dtd (an XML::Twig::DTD object) of a twig
xmldecl Return the XML declaration for the document, or a default one if it doesn’t have one
doctype Return the doctype for the document
doctype_name returns the doctype of the document from the doctype declaration
system_id returns the system value of the DTD of the document from the doctype declaration
public_id returns the public doctype of the document from the doctype declaration
internal_subset returns the internal subset of the DTD
dtd_text Return the DTD text
dtd_print Print the DTD
model ($tag) Return the model (in the DTD) for the element CW$tag
root Return the root element of a twig
set_root ($elt) Set the root of a twig
first_elt ($optional_condition) Return the first element matching CW$optional_condition of a twig, if no condition is given then the root is returned
last_elt ($optional_condition) Return the last element matching CW$optional_condition of a twig, if no condition is given then the last element of the twig is returned
elt_id ($id) Return the element whose CWid attribute is CW$id
getEltById Same as CWelt_id
index ($index_name, CW$optional_index) If the CW$optional_index argument is present, return the corresponding element in the index (created using the CWindex option for CWXML::Twig-new>)

If the argument is not present, return an arrayref to the index

normalize merge together all consecutive pcdata elements in the document (if for example you have turned some elements into pcdata using CWerase, this will give you a clean document in which there all text elements are as long as possible).
encoding This method returns the encoding of the XML document, as defined by the CWencoding attribute in the XML declaration (ie it is CWundef if the attribute is not defined)
set_encoding This method sets the value of the CWencoding attribute in the XML declaration. Note that if the document did not have a declaration it is generated (with an XML version of 1.0)
xml_version This method returns the XML version, as defined by the CWversion attribute in the XML declaration (ie it is CWundef if the attribute is not defined)
set_xml_version This method sets the value of the CWversion attribute in the XML declaration. If the declaration did not exist it is created.
standalone This method returns the value of the CWstandalone declaration for the document
set_standalone This method sets the value of the CWstandalone attribute in the XML declaration. Note that if the document did not have a declaration it is generated (with an XML version of 1.0)
set_output_encoding Set the CWencoding attribute in the XML declaration
set_doctype ($name, CW$system, CW$public, CW$internal) Set the doctype of the element. If an argument is CWundef (or not present) then its former value is retained, if a false (’’ or 0) value is passed then the former value is deleted;
entity_list Return the entity list of a twig
entity_names Return the list of all defined entities
entity ($entity_name) Return the entity
change_gi ($old_gi, CW$new_gi) Performs a (very fast) global change. All elements CW$old_gi are now CW$new_gi. This is a bit dangerous though and should be avoided if < possible, as the new tag might be ignored in subsequent processing.

See CWBUGS

flush ($optional_filehandle, CW%options) Flushes a twig up to (and including) the current element, then deletes all unnecessary elements from the tree that’s kept in memory. CWflush keeps track of which elements need to be open/closed, so if you flush from handlers you don’t have to worry about anything. Just keep flushing the twig every time you’re done with a sub-tree and it will come out well-formed. After the whole parsing don’t forget toCWflush one more time to print the end of the document. The doctype and entity declarations are also printed.

flush take an optional filehandle as an argument.

options: use the CWupdate_DTD option if you have updated the (internal) DTD and/or the entity list and you want the updated DTD to be output

The CWpretty_print option sets the pretty printing of the document.



   Example: $t->flush( Update_DTD => 1);
            $t->flush( $filehandle, pretty_print => indented);
            $t->flush( \*FILE);



flush_up_to ($elt, CW$optional_filehandle, CW%options) Flushes up to the CW$elt element. This allows you to keep part of the tree in memory when you CWflush.

options: see flush.

purge Does the same as a CWflush except it does not print the twig. It just deletes all elements that have been completely parsed so far.
purge_up_to ($elt) Purges up to the CW$elt element. This allows you to keep part of the tree in memory when you CWpurge.
print ($optional_filehandle, CW%options) Prints the whole document associated with the twig. To be used only AFTER the parse.

options: see CWflush.

print_to_file ($filename, CW%options) Prints the whole document associated with the twig to file CW$filename. To be used only AFTER the parse.

options: see CWflush.

sprint Return the text of the whole document associated with the twig. To be used only AFTER the parse.

options: see CWflush.

trim Trim the document: gets rid of initial and trailing spaces, and replaces multiple spaces by a single one.
toSAX1 ($handler) Send SAX events for the twig to the SAX1 handler CW$handler
toSAX2 ($handler) Send SAX events for the twig to the SAX2 handler CW$handler
flush_toSAX1 ($handler) Same as flush, except that SAX events are sent to the SAX1 handler CW$handler instead of the twig being printed
flush_toSAX2 ($handler) Same as flush, except that SAX events are sent to the SAX2 handler CW$handler instead of the twig being printed
ignore This method should be called during parsing, usually in CWstart_tag_handlers. It causes the element to be skipped during the parsing: the twig is not built for this element, it will not be accessible during parsing or after it. The element will not take up any memory and parsing will be faster.

Note that this method can also be called on an element. If the element is a parent of the current element then this element will be ignored (the twig will not be built any more for it and what has already been built will be deleted).

set_pretty_print ($style) Set the pretty print method, amongst ’CWnone’ (default), ’CWnsgmls’, ’CWnice’, ’CWindented’, CWindented_c, ’CWwrapped’, ’CWrecord’ and ’CWrecord_c

WARNING: the pretty print style is a GLOBAL variable, so once set it’s applied to ALL CWprint’s (and CWsprint’s). Same goes if you use XML::Twig with CWmod_perl . This should not be a problem as the XML that’s generated is valid anyway, and XML processors (as well as HTML processors, including browsers) should not care. Let me know if this is a big problem, but at the moment the performance/cleanliness trade-off clearly favors the global approach.

set_empty_tag_style ($style) Set the empty tag display style (’CWnormal’, ’CWhtml’ or ’CWexpand’). As with CWset_pretty_print this sets a global flag.

CWnormal outputs an empty tag ’CW<tag/>’, CWhtml adds a space ’CW<tag />’ for elements that can be empty in XHTML and CWexpand outputs ’CW<tag></tag>

set_remove_cdata ($flag) set (or unset) the flag that forces the twig to output CDATA sections as regular (escaped) PCDATA
print_prolog ($optional_filehandle, CW%options) Prints the prolog (XML declaration + DTD + entity declarations) of a document.

options: see CWflush.

prolog ($optional_filehandle, CW%options) Return the prolog (XML declaration + DTD + entity declarations) of a document.

options: see CWflush.

finish Call Expat CWfinish method. Unsets all handlers (including internal ones that set context), but expat continues parsing to the end of the document or until it finds an error. It should finish up a lot faster than with the handlers set.
finish_print Stops twig processing, flush the twig and proceed to finish printing the document as fast as possible. Use this method when modifying a document and the modification is done.
finish_now Stops twig processing, does not finish parsing the document (which could actually be not well-formed after the point where CWfinish_now is called). Execution resumes after the CWLparse> or CWparsefile call. The content of the twig is what has been parsed so far (all open elements at the time CWfinish_now is called are considered closed).
set_expand_external_entities Same as using the CWexpand_external_ents option when creating the twig
set_input_filter Same as using the CWinput_filter option when creating the twig
set_keep_atts_order Same as using the CWkeep_atts_order option when creating the twig
set_keep_encoding Same as using the CWkeep_encoding option when creating the twig
escape_gt usually XML::Twig does not escape > in its output. Using this option makes it replace > by >
do_not_escape_gt reverts XML::Twig behavior to its default of not escaping > in its output.
set_output_filter Same as using the CWoutput_filter option when creating the twig
set_output_text_filter Same as using the CWoutput_text_filter option when creating the twig
add_stylesheet ($type, CW@options) Adds an external stylesheet to an XML document.

Supported types and options:
xsl option: the url of the stylesheet

Example:



  $t->add_stylesheet( xsl => "xsl_style.xsl");



will generate the following PI at the beginning of the document:



  <?xml-stylesheet type="text/xsl" href="xsl_style.xsl"?>



css option: the url of the stylesheet

Methods inherited from XML::Parser::Expat A twig inherits all the relevant methods from XML::Parser::Expat. These methods can only be used during the parsing phase (they will generate a fatal error otherwise).

Inherited methods are:
depth Returns the size of the context list.
in_element Returns true if NAME is equal to the name of the innermost currently opened element. If namespace processing is being used and you want to check against a name that may be in a namespace, then use the generate_ns_name method to create the NAME argument.
within_element Returns the number of times the given name appears in the context list. If namespace processing is being used and you want to check against a name that may be in a namespace, then use the generate_ns_name method to create the NAME argument.
context Returns a list of element names that represent open elements, with the last one being the innermost. Inside start and end tag handlers, this will be the tag of the parent element.
current_line Returns the line number of the current position of the parse.
current_column Returns the column number of the current position of the parse.
current_byte Returns the current position of the parse.
position_in_context Returns a string that shows the current parse position. LINES should be an integer >= 0 that represents the number of lines on either side of the current parse line to place into the returned string.
base ([NEWBASE]) Returns the current value of the base for resolving relative URIs. If NEWBASE is supplied, changes the base to that value.
current_element Returns the name of the innermost currently opened element. Inside start or end handlers, returns the parent of the element associated with those tags.
element_index Returns an integer that is the depth-first visit order of the current element. This will be zero outside of the root element. For example, this will return 1 when called from the start handler for the root element start tag.
recognized_string Returns the string from the document that was recognized in order to call the current handler. For instance, when called from a start handler, it will give us the the start-tag string. The string is encoded in UTF-8. This method doesn’t return a meaningful string inside declaration handlers.
original_string Returns the verbatim string from the document that was recognized in order to call the current handler. The string is in the original document encoding. This method doesn’t return a meaningful string inside declaration handlers.
xpcroak Concatenate onto the given message the current line number within the XML document plus the message implied by ErrorContext. Then croak with the formed message.
xpcarp Concatenate onto the given message the current line number within the XML document plus the message implied by ErrorContext. Then carp with the formed message.
xml_escape(TEXT [, CHAR [, CHAR ...]]) Returns TEXT with markup characters turned into character entities. Any additional characters provided as arguments are also turned into character references where found in TEXT.

(this method is broken on some versions of expat/XML::Parser)

path ( CW$optional_tag) Return the element context in a form similar to XPath’s short form: ’CW/root/tag1/../tag
get_xpath ( CW$optional_array_ref, CW$xpath, CW$optional_offset) Performs a CWget_xpath on the document root (see <Elt|Elt>)

If the CW$optional_array_ref argument is used the array must contain elements. The CW$xpath expression is applied to each element in turn and the result is union of all results. This way a first query can be refined in further steps.

find_nodes ( CW$optional_array_ref, CW$xpath, CW$optional_offset) same as CWget_xpath
findnodes ( CW$optional_array_ref, CW$xpath, CW$optional_offset) same as CWget_xpath (similar to the XML::LibXML method)
findvalue ( CW$optional_array_ref, CW$xpath, CW$optional_offset) Return the CWjoin of all texts of the results of applying CWget_xpath to the node (similar to the XML::LibXML method)
subs_text ($regexp, CW$replace) subs_text does text substitution on the whole document, similar to perl’s CW s/// operator.
dispose Useful only if you don’t have CWScalar::Util or CWWeakRef installed.

Reclaims properly the memory used by an XML::Twig object. As the object has circular references it never goes out of scope, so if you want to parse lots of XML documents then the memory leak becomes a problem. Use CW$twig->dispose to clear this problem.

create_accessors (list_of_attribute_names) A convenience method that creates l-valued accessors for attributes. So CW$twig->create_accessors( foo) will create a CWfoo method that can be called on elements:



  $elt->foo;         # equivalent to $elt->{att}->{foo};
  $elt->foo( bar); # equivalent to $elt->set_att( foo => bar);



set_do_not_escape_amp_in_atts An evil method, that I only document because Test::Pod::Coverage complaints otherwise, but really, you don’t want to know about it.

    XML::Twig::Elt

new ($optional_tag, CW$optional_atts, CW@optional_content) The CWtag is optional (but then you can’t have a content ), the CW$optional_atts argument is a reference to a hash of attributes, the content can be just a string or a list of strings and element. A content of ’CW#EMPTY’ creates an empty element;



 Examples: my $elt= XML::Twig::Elt->new();
           my $elt= XML::Twig::Elt->new( para => { align => center }); 
           my $elt= XML::Twig::Elt->new( para => { align => center }, foo); 
           my $elt= XML::Twig::Elt->new( br   => #EMPTY);
           my $elt= XML::Twig::Elt->new( para);
           my $elt= XML::Twig::Elt->new( para => this is a para); 
           my $elt= XML::Twig::Elt->new( para => $elt3, another para);



The strings are not parsed, the element is not attached to any twig.

WARNING: if you rely on ID’s then you will have to set the id yourself. At this point the element does not belong to a twig yet, so the ID attribute is not known so it won’t be stored in the ID list.

Note that CW#COMMENT, CW#PCDATA or CW#CDATA are valid tag names, that will create text elements.

To create an element CWfoo containing a CDATA section:



           my $foo= XML::Twig::Elt->new( #CDATA => "content of the CDATA section")
                                  ->wrap_in( foo);



An attribute of ’#CDATA’, will create the content of the element as CDATA:



  my $elt= XML::Twig::Elt->new( p => { #CDATA => 1}, foo < bar);



creates an element



  <p><![CDATA[foo < bar]]></>



parse ($string, CW%args) Creates an element from an XML string. The string is actually parsed as a new twig, then the root of that twig is returned. The arguments in CW%args are passed to the twig. As always if the parse fails the parser will die, so use an eval if you want to trap syntax errors.

As obviously the element does not exist beforehand this method has to be called on the class:



  my $elt= parse XML::Twig::Elt( "<a> string to parse, with <sub/>
                                  <elements>, actually tons of </elements>
                  h</a>");



set_inner_xml ($string) Sets the content of the element to be the tree created from the string
set_inner_html ($string) Sets the content of the element, after parsing the string with an HTML parser (HTML::Parser)
print ($optional_filehandle, CW$optional_pretty_print_style) Prints an entire element, including the tags, optionally to a CW$optional_filehandle, optionally with a CW$pretty_print_style.

The print outputs XML data so base entities are escaped.

sprint ($elt, CW$optional_no_enclosing_tag) Return the xml string for an entire element, including the tags. If the optional second argument is true then only the string inside the element is returned (the start and end tag for CW$elt are not). The text is XML-escaped: base entities (& and < in text, & < and " in attribute values) are turned into entities.
gi Return the gi of the element (the gi is the CWgeneric identifier the tag name in SGML parlance).

CWtag and CWname are synonyms of CWgi.

tag Same as CWgi
name Same as CWtag
set_gi ($tag) Set the gi (tag) of an element
set_tag ($tag) Set the tag (=CWtag) of an element
set_name ($name) Set the name (=CWtag) of an element
root Return the root of the twig in which the element is contained.
twig Return the twig containing the element.
parent ($optional_condition) Return the parent of the element, or the first ancestor matching the CW$optional_condition
first_child ($optional_condition) Return the first child of the element, or the first child matching the CW$optional_condition
has_child ($optional_condition) Return the first child of the element, or the first child matching the CW$optional_condition (same as first_child)
has_children ($optional_condition) Return the first child of the element, or the first child matching the CW$optional_condition (same as first_child)
first_child_text ($optional_condition) Return the text of the first child of the element, or the first child
matching the CW$optional_condition If there is no first_child then returns ’’. This avoids getting the child, checking for its existence then getting the text for trivial cases.

Similar methods are available for the other navigation methods:
last_child_text
prev_sibling_text
next_sibling_text
prev_elt_text
next_elt_text
child_text
parent_text

All this methods also exist in trimmed variant:
first_child_trimmed_text
last_child_trimmed_text
prev_sibling_trimmed_text
next_sibling_trimmed_text
prev_elt_trimmed_text
next_elt_trimmed_text
child_trimmed_text
parent_trimmed_text

field ($condition) Same method as CWfirst_child_text with a different name
fields ($condition_list) Return the list of field (text of first child matching the conditions), missing fields are returned as the empty string.

Same method as CWfirst_child_text with a different name

trimmed_field ($optional_condition) Same method as CWfirst_child_trimmed_text with a different name
set_field ($condition, CW$optional_atts, CW@list_of_elt_and_strings) Set the content of the first child of the element that matches CW$condition, the rest of the arguments is the same as for CWset_content

If no child matches CW$condition _and_ if CW$condition is a valid XML element name, then a new element by that name is created and inserted as the last child.

first_child_matches ($optional_condition) Return the element if the first child of the element (if it exists) passes the CW$optional_condition CWundef otherwise



  if( $elt->first_child_matches( title)) ...



is equivalent to



  if( $elt->{first_child} && $elt->{first_child}->passes( title))



CWfirst_child_is is another name for this method

Similar methods are available for the other navigation methods:
last_child_matches
prev_sibling_matches
next_sibling_matches
prev_elt_matches
next_elt_matches
child_matches
parent_matches

is_first_child ($optional_condition) returns true (the element) if the element is the first child of its parent (optionally that satisfies the CW$optional_condition)
is_last_child ($optional_condition) returns true (the element) if the element is the last child of its parent (optionally that satisfies the CW$optional_condition)
prev_sibling ($optional_condition) Return the previous sibling of the element, or the previous sibling matching CW$optional_condition
next_sibling ($optional_condition) Return the next sibling of the element, or the first one matching CW$optional_condition.
next_elt ($optional_elt, CW$optional_condition) Return the next elt (optionally matching CW$optional_condition) of the element. This is defined as the next element which opens after the current element opens. Which usually means the first child of the element. Counter-intuitive as it might look this allows you to loop through the whole document by starting from the root.

The CW$optional_elt is the root of a subtree. When the CWnext_elt is out of the subtree then the method returns undef. You can then walk a sub tree with:



  my $elt= $subtree_root;
  while( $elt= $elt->next_elt( $subtree_root)
    { # insert processing code here
    }



prev_elt ($optional_condition) Return the previous elt (optionally matching CW$optional_condition) of the element. This is the first element which opens before the current one. It is usually either the last descendant of the previous sibling or simply the parent
next_n_elt ($offset, CW$optional_condition) Return the CW$offset-th element that matches the CW$optional_condition
following_elt Return the following element (as per the XPath following axis)
preceding_elt Return the preceding element (as per the XPath preceding axis)
following_elts Return the list of following elements (as per the XPath following axis)
preceding_elts Return the pst of preceding elements (as per the XPath preceding axis)
children ($optional_condition) Return the list of children (optionally which matches CW$optional_condition) of the element. The list is in document order.
children_count ($optional_condition) Return the number of children of the element (optionally which matches CW$optional_condition)
children_text ($optional_condition) In array context, reeturns an array containing the text of children of the element (optionally which matches CW$optional_condition)

In scalar context, returns the concatenation of the text of children of the element

children_trimmed_text ($optional_condition) In array context, returns an array containing the trimmed text of children of the element (optionally which matches CW$optional_condition)

In scalar context, returns the concatenation of the trimmed text of children of the element

children_copy ($optional_condition) Return a list of elements that are copies of the children of the element, optionally which matches CW$optional_condition
descendants ($optional_condition) Return the list of all descendants (optionally which matches CW$optional_condition) of the element. This is the equivalent of the CWgetElementsByTagName of the DOM (by the way, if you are really a DOM addict, you can use CWgetElementsByTagName instead)
getElementsByTagName ($optional_condition) Same as CWdescendants
find_by_tag_name ($optional_condition) Same as CWdescendants
descendants_or_self ($optional_condition) Same as CWdescendants except that the element itself is included in the list if it matches the CW$optional_condition
first_descendant ($optional_condition) Return the first descendant of the element that matches the condition
last_descendant ($optional_condition) Return the last descendant of the element that matches the condition
ancestors ($optional_condition) Return the list of ancestors (optionally matching CW$optional_condition) of the element. The list is ordered from the innermost ancestor to the outermost one

NOTE: the element itself is not part of the list, in order to include it you will have to use ancestors_or_self

ancestors_or_self ($optional_condition) Return the list of ancestors (optionally matching CW$optional_condition) of the element, including the element (if it matches the condition>). The list is ordered from the innermost ancestor to the outermost one
passes ($condition) Return the element if it passes the CW$condition
att ($att) Return the value of attribute CW$att or CWundef
set_att ($att, CW$att_value) Set the attribute of the element to the given value

You can actually set several attributes this way:



  $elt->set_att( att1 => "val1", att2 => "val2");



del_att ($att) Delete the attribute for the element

You can actually delete several attributes at once:



  $elt->del_att( att1, att2, att3);



att_exists ($att) Returns true if the attribute CW$att exists for the element, false otherwise
cut Cut the element from the tree. The element still exists, it can be copied or pasted somewhere else, it is just not attached to the tree anymore.

Note that the old links to the parent, previous and next siblings can still be accessed using the former_* methods

former_next_sibling Returns the former next sibling of a cut node (or undef if the node has not been cut)

This makes it easier to write loops where you cut elements:



    my $child= $parent->first_child( achild);
    while( $child->{att}->{cut})
      { $child->cut; $child= $child->former_next_sibling; }



former_prev_sibling Returns the former previous sibling of a cut node (or undef if the node has not been cut)
former_parent Returns the former parent of a cut node (or undef if the node has not been cut)
cut_children ($optional_condition) Cut all the children of the element (or all of those which satisfy the CW$optional_condition).

Return the list of children

copy ($elt) Return a copy of the element. The copy is a deep copy: all sub elements of the element are duplicated.
paste ($optional_position, CW$ref) Paste a (previously CWcut or newly generated) element. Die if the element already belongs to a tree.

Note that the calling element is pasted:



  $child->paste( first_child => $existing_parent);
  $new_sibling->paste( after => $this_sibling_is_already_in_the_tree);



or



  my $new_elt= XML::Twig::Elt->new( tag => $content);
  $new_elt->paste( $position => $existing_elt);



Example:



  my $t= XML::Twig->new->parse( doc.xml)
  my $toc= $t->root->new( toc);
  $toc->paste( $t->root); # $toc is pasted as first child of the root
  foreach my $title ($t->findnodes( /doc/section/title))
    { my $title_toc= $title->copy;
      # paste $title_toc as the last child of toc
      $title_toc->paste( last_child => $toc)
    }



Position options:
first_child (default) The element is pasted as the first child of CW$ref
last_child The element is pasted as the last child of CW$ref
before The element is pasted before CW$ref, as its previous sibling.
after The element is pasted after CW$ref, as its next sibling.
within In this case an extra argument, CW$offset, should be supplied. The element will be pasted in the reference element (or in its first text child) at the given offset. To achieve this the reference element will be split at the offset.

Note that you can call directly the underlying method:
paste_before
paste_after
paste_first_child
paste_last_child
paste_within

move ($optional_position, CW$ref) Move an element in the tree. This is just a CWcut then a CWpaste. The syntax is the same as CWpaste.
replace ($ref) Replaces an element in the tree. Sometimes it is just not possible toCWcut an element then CWpaste another in its place, so CWreplace comes in handy. The calling element replaces CW$ref.
replace_with (@elts) Replaces the calling element with one or more elements
delete Cut the element and frees the memory.
prefix ($text, CW$optional_option) Add a prefix to an element. If the element is a CWPCDATA element the text is added to the pcdata, if the elements first child is a CWPCDATA then the text is added to it’s pcdata, otherwise a new CWPCDATA element is created and pasted as the first child of the element.

If the option is CWasis then the prefix is added asis: it is created in a separate CWPCDATA element with an CWasis property. You can then write:



  $elt1->prefix( <b>, asis);



to create a CW<b> in the output of CWprint.

suffix ($text, CW$optional_option) Add a suffix to an element. If the element is a CWPCDATA element the text is added to the pcdata, if the elements last child is a CWPCDATA then the text is added to it’s pcdata, otherwise a new PCDATA element is created and pasted as the last child of the element.

If the option is CWasis then the suffix is added asis: it is created in a separate CWPCDATA element with an CWasis property. You can then write:



  $elt2->suffix( </b>, asis);



trim Trim the element in-place: spaces at the beginning and at the end of the element are discarded and multiple spaces within the element (or its descendants) are replaced by a single space.

Note that in some cases you can still end up with multiple spaces, if they are split between several elements:



  <doc>  text <b>  hah! </b>  yep</doc>



gets trimmed to



  <doc>text <b> hah! </b> yep</doc>



This is somewhere in between a bug and a feature.

normalize merge together all consecutive pcdata elements in the element (if for example you have turned some elements into pcdata using CWerase, this will give you a clean element in which there all text fragments are as long as possible).
simplify (%options) Return a data structure suspiciously similar to XML::Simple’s. Options are identical to XMLin options, see XML::Simple doc for more details (or use DATA::dumper or YAML to dump the data structure)
content_key
forcearray
keyattr
noattr
normalize_space aka normalise_space
variables (%var_hash) CW%var_hash is a hash { name => value }

This option allows variables in the XML to be expanded when the file is read. (there is no facility for putting the variable names back if you regenerate XML using XMLout).

A ’variable’ is any text of the form ${name} (or CW$name) which occurs in an attribute value or in the text content of an element. If ’name’ matches a key in the supplied hashref, ${name} will be replaced with the corresponding value from the hashref. If no matching key is found, the variable will not be replaced.

var_att ($attribute_name) This option gives the name of an attribute that will be used to create variables in the XML:



  <dirs>
    <dir name="prefix">/usr/local</dir>
    <dir name="exec_prefix">$prefix/bin</dir>
  </dirs>



use CWvar => name to get CW$prefix replaced by /usr/local in the generated data structure

By default variables are captured by the following regexp: /$(\w+)/

var_regexp (regexp) This option changes the regexp used to capture variables. The variable name should be in CW$1
group_tags { grouping tag => grouped tag, grouping tag 2 => grouped tag 2...} Option used to simplify the structure: elements listed will not be used. Their children will be, they will be considered children of the element parent.

If the element is:



  <config host="laptop.xmltwig.com">
    <server>localhost</server>
    <dirs>
      <dir name="base">/home/mrodrigu/standards</dir>
      <dir name="tools">$base/tools</dir>
    </dirs>
    <templates>
      <template name="std_def">std_def.templ</template>
      <template name="dummy">dummy</template>
    </templates>
  </config>



Then calling simplify with CWgroup_tags => { dirs => dir, templates => template} makes the data structure be exactly as if the start and end tags for CWdirs and CWtemplates were not there.

A YAML dump of the structure



  base: /home/mrodrigu/standards
  host: laptop.xmltwig.com
  server: localhost
  template:
    - std_def.templ
    - dummy.templ
  tools: $base/tools



split_at ($offset) Split a text (CWPCDATA or CWCDATA) element in 2 at CW$offset, the original element now holds the first part of the string and a new element holds the right part. The new element is returned

If the element is not a text element then the first text child of the element is split

split ( CW$optional_regexp, CW$tag1, CW$atts1, CW$tag2, CW$atts2...) Split the text descendants of an element in place, the text is split using the CW$regexp, if the regexp includes () then the matched separators will be wrapped in elements. CW$1 is wrapped in CW$tag1, with attributes CW$atts1 if CW$atts1 is given (as a hashref), CW$2 is wrapped in CW$tag2...

if CW$elt is CW<p>tati tata <b>tutu tati titi</b> tata tati tata</p>



  $elt->split( qr/(ta)ti/, foo, {type => toto} )



will change CW$elt to



  <p><foo type="toto">ta</foo> tata <b>tutu <foo type="toto">ta</foo>
      titi</b> tata <foo type="toto">ta</foo> tata</p>



The regexp can be passed either as a string or as CWqr// (perl 5.005 and later), it defaults to \s+ just as the CWsplit built-in (but this would be quite a useless behaviour without the CW$optional_tag parameter)

CW$optional_tag defaults to PCDATA or CDATA, depending on the initial element type

The list of descendants is returned (including un-touched original elements and newly created ones)

mark ( CW$regexp, CW$optional_tag, CW$optional_attribute_ref) This method behaves exactly as split, except only the newly created elements are returned
wrap_children ( CW$regexp_string, CW$tag, CW$optional_attribute_hashref) Wrap the children of the element that match the regexp in an element CW$tag. If CW$optional_attribute_hashref is passed then the new element will have these attributes.

The CW$regexp_string includes tags, within pointy brackets, as in CW<title><para>+ and the usual Perl modifiers (+*?...). Tags can be further qualified with attributes: CW<para type="warning" classif="cosmic_secret">+. The values for attributes should be xml-escaped: CW<candy type="M&Ms">* (CW<, CW& CB> and CW" should be escaped).

Note that elements might get extra CWid attributes in the process. See add_id. Use strip_att to remove unwanted id’s.

Here is an example:

If the element CW$elt has the following content:



  <elt>
   <p>para 1</p>
   <l_l1_1>list 1 item 1 para 1</l_l1_1>
     <l_l1>list 1 item 1 para 2</l_l1>
   <l_l1_n>list 1 item 2 para 1 (only para)</l_l1_n>
   <l_l1_n>list 1 item 3 para 1</l_l1_n>
     <l_l1>list 1 item 3 para 2</l_l1>
     <l_l1>list 1 item 3 para 3</l_l1>
   <l_l1_1>list 2 item 1 para 1</l_l1_1>
     <l_l1>list 2 item 1 para 2</l_l1>
   <l_l1_n>list 2 item 2 para 1 (only para)</l_l1_n>
   <l_l1_n>list 2 item 3 para 1</l_l1_n>
     <l_l1>list 2 item 3 para 2</l_l1>
     <l_l1>list 2 item 3 para 3</l_l1>
  </elt>



Then the code



  $elt->wrap_children( q{<l_l1_1><l_l1>*} , li => { type => "ul1" });
  $elt->wrap_children( q{<l_l1_n><l_l1>*} , li => { type => "ul" });

  $elt->wrap_children( q{<li type="ul1"><li type="ul">+}, "ul");
  $elt->strip_att( id);
  $elt->strip_att( type);
  $elt->print;



will output:



  <elt>
     <p>para 1</p>
     <ul>
       <li>
         <l_l1_1>list 1 item 1 para 1</l_l1_1>
         <l_l1>list 1 item 1 para 2</l_l1>
       </li>
       <li>
         <l_l1_n>list 1 item 2 para 1 (only para)</l_l1_n>
       </li>
       <li>
         <l_l1_n>list 1 item 3 para 1</l_l1_n>
         <l_l1>list 1 item 3 para 2</l_l1>
         <l_l1>list 1 item 3 para 3</l_l1>
       </li>
     </ul>
     <ul>
       <li>
         <l_l1_1>list 2 item 1 para 1</l_l1_1>
         <l_l1>list 2 item 1 para 2</l_l1>
       </li>
       <li>
         <l_l1_n>list 2 item 2 para 1 (only para)</l_l1_n>
       </li>
       <li>
         <l_l1_n>list 2 item 3 para 1</l_l1_n>
         <l_l1>list 2 item 3 para 2</l_l1>
         <l_l1>list 2 item 3 para 3</l_l1>
       </li>
     </ul>
  </elt>



subs_text ($regexp, CW$replace) subs_text does text substitution, similar to perl’s CW s/// operator.

CW$regexp must be a perl regexp, created with the CWqr operator.

CW$replace can include CW$1, $2... from the CW$regexp. It can also be used to create element and entities, by using CW&elt( tag => { att => val }, text) (similar syntax as CWnew) and CW&ent( name).

Here is a rather complex example:



  $elt->subs_text( qr{(?<!do not )link to (http://([^\s,]*))},
                   see &elt( a =>{ href => $1 }, $2)
                 );



This will replace text like link to http://www.xmltwig.com by see <a href=www.xmltwig.com>www.xmltwig.com</a>, but not do not link to...

Generating entities (here replacing spaces with  ):



  $elt->subs_text( qr{ }, &ent( " "));



or, using a variable:



  my $ent=" ";
  $elt->subs_text( qr{ }, "&ent( $ent)");



Note that the substitution is always global, as in using the CWg modifier in a perl substitution, and that it is performed on all text descendants of the element.

Bug: in the CW$regexp, you can only use CW\1, CW\2... if the replacement expression does not include elements or attributes. eg



  t->subs_text( qr/((t[aiou])\2)/, $2);             # ok, replaces toto, tata, titi, tutu by to, ta, ti, tu
  t->subs_text( qr/((t[aiou])\2)/, &elt(p => $1) ); # NOK, does not find toto...



add_id ($optional_coderef) Add an id to the element.

The id is an attribute, CWid by default, see the CWid option for XML::Twig CWnew to change it. Use an id starting with CW# to get an id that’s not output by print, flush or sprint, yet that allows you to use the elt_id method to get the element easily.

If the element already has an id, no new id is generated.

By default the method create an id of the form CWtwig_id_<nnnn>, where CW<nnnn> is a number, incremented each time the method is called successfully.

set_id_seed ($prefix) by default the id generated by CWadd_id is CWtwig_id_<nnnn>, CWset_id_seed changes the prefix to CW$prefix and resets the number to 1
strip_att ($att) Remove the attribute CW$att from all descendants of the element (including the element)

Return the element

change_att_name ($old_name, CW$new_name) Change the name of the attribute from CW$old_name to CW$new_name. If there is no attribute CW$old_name nothing happens.
lc_attnames Lower cases the name all the attributes of the element.
sort_children_on_value( CW%options) Sort the children of the element in place according to their text. All children are sorted.

Return the element, with its children sorted.

CW%options are



  type  : numeric |  alpha     (default: alpha)
  order : normal  |  reverse   (default: normal)



Return the element, with its children sorted

sort_children_on_att ($att, CW%options) Sort the children of the element in place according to attribute CW$att. CW%options are the same as for CWsort_children_on_value

Return the element.

sort_children_on_field ($tag, CW%options) Sort the children of the element in place, according to the field CW$tag (the text of the first child of the child with this tag). CW%options are the same as for CWsort_children_on_value.

Return the element, with its children sorted

sort_children( CW$get_key, CW%options) Sort the children of the element in place. The CW$get_key argument is a reference to a function that returns the sort key when passed an element.

For example:



  $elt->sort_children( sub { $_[0]->{att}->{"nb"} + $_[0]->text },
                       type => numeric, order => reverse
                     );



field_to_att ($cond, CW$att) Turn the text of the first sub-element matched by CW$cond into the value of attribute CW$att of the element. If CW$att is omitted then CW$cond is used as the name of the attribute, which makes sense only if CW$cond is a valid element (and attribute) name.

The sub-element is then cut.

att_to_field ($att, CW$tag) Take the value of attribute CW$att and create a sub-element CW$tag as first child of the element. If CW$tag is omitted then CW$att is used as the name of the sub-element.
get_xpath ($xpath, CW$optional_offset) Return a list of elements satisfying the CW$xpath. CW$xpath is an XPATH-like expression.

A subset of the XPATH abbreviated syntax is covered:



  tag
  tag[1] (or any other positive number)
  tag[last()]
  tag[@att] (the attribute exists for the element)
  tag[@att="val"]
  tag[@att=~ /regexp/]
  tag[att1="val1" and att2="val2"]
  tag[att1="val1" or att2="val2"]
  tag[string()="toto"] (returns tag elements which text (as per the text method)
                       is toto)
  tag[string()=~/regexp/] (returns tag elements which text (as per the text
                          method) matches regexp)
  expressions can start with / (search starts at the document root)
  expressions can start with . (search starts at the current element)
  // can be used to get all descendants instead of just direct children
  * matches any tag



So the following examples from the XPath recommendation<http://www.w3.org/TR/xpath.html#path-abbrev> work:



  para selects the para element children of the context node
  * selects all element children of the context node
  para[1] selects the first para child of the context node
  para[last()] selects the last para child of the context node
  */para selects all para grandchildren of the context node
  /doc/chapter[5]/section[2] selects the second section of the fifth chapter
     of the doc
  chapter//para selects the para element descendants of the chapter element
     children of the context node
  //para selects all the para descendants of the document root and thus selects
     all para elements in the same document as the context node
  //olist/item selects all the item elements in the same document as the
     context node that have an olist parent
  .//para selects the para element descendants of the context node
  .. selects the parent of the context node
  para[@type="warning"] selects all para children of the context node that have
     a type attribute with value warning
  employee[@secretary and @assistant] selects all the employee children of the
     context node that have both a secretary attribute and an assistant
     attribute



The elements will be returned in the document order.

If CW$optional_offset is used then only one element will be returned, the one with the appropriate offset in the list, starting at 0

Quoting and interpolating variables can be a pain when the Perl syntax and the XPATH syntax collide, so use alternate quoting mechanisms like q or qq (I like q{} and qq{} myself).

Here are some more examples to get you started:



  my $p1= "p1";
  my $p2= "p2";
  my @res= $t->get_xpath( qq{p[string( "$p1") or string( "$p2")]});

  my $a= "a1";
  my @res= $t->get_xpath( qq{//*[@att="$a"]});

  my $val= "a1";
  my $exp= qq{//p[ \@att=$val]}; # you need to use \@ or you will get a warning
  my @res= $t->get_xpath( $exp);



Note that the only supported regexps delimiters are / and that you must backslash all / in regexps AND in regular strings.

XML::Twig does not provide natively full XPATH support, but you can use CWXML::Twig::XPath to get CWfindnodes to use CWXML::XPath as the XPath engine, with full coverage of the spec.

CWXML::Twig::XPath to get CWfindnodes to use CWXML::XPath as the XPath engine, with full coverage of the spec.

find_nodes same asCWget_xpath
findnodes same as CWget_xpath
text CW@optional_options Return a string consisting of all the CWPCDATA and CWCDATA in an element, without any tags. The text is not XML-escaped: base entities such as CW& and CW< are not escaped.

The ’CWno_recurse’ option will only return the text of the element, not of any included sub-elements (same as CWtext_only).

text_only Same as CWtext except that the text returned doesn’t include the text of sub-elements.
trimmed_text Same as CWtext except that the text is trimmed: leading and trailing spaces are discarded, consecutive spaces are collapsed
set_text ($string) Set the text for the element: if the element is a CWPCDATA, just set its text, otherwise cut all the children of the element and create a single CWPCDATA child for it, which holds the text.
merge ($elt2) Move the content of CW$elt2 within the element
insert ($tag1, [$optional_atts1], CW$tag2, [$optional_atts2],...) For each tag in the list inserts an element CW$tag as the only child of the element. The element gets the optional attributes inCW$optional_atts<n>. All children of the element are set as children of the new element. The upper level element is returned.



  $p->insert( table => { border=> 1}, tr, td)



put CW$p in a table with a visible border, a single CWtr and a single CWtd and return the CWtable element:



  <p><table border="1"><tr><td>original content of p</td></tr></table></p>



wrap_in (@tag) Wrap elements in CW@tag as the successive ancestors of the element, returns the new element. CW$elt->wrap_in( td, tr, table) wraps the element as a single cell in a table for example.

Optionally each tag can be followed by a hashref of attributes, that will be set on the wrapping element:



  $elt->wrap_in( p => { class => "advisory" }, div => { class => "intro", id => "div_intro });



insert_new_elt ($opt_position, CW$tag, CW$opt_atts_hashref, CW@opt_content) Combines a CWnew and a CWpaste : creates a new element using CW$tag, CW$opt_atts_hashref and CW@opt_content which are arguments similar to those for CWnew, then paste it, using CW$opt_position or CWfirst_child, relative to CW$elt.

Return the newly created element

erase Erase the element: the element is deleted and all of its children are pasted in its place.
set_content ( CW$optional_atts, CW@list_of_elt_and_strings) ( CW$optional_atts, ’#EMPTY’) Set the content for the element, from a list of strings and elements. Cuts all the element children, then pastes the list elements as the children. This method will create a CWPCDATA element for any strings in the list.

The CW$optional_atts argument is the ref of a hash of attributes. If this argument is used then the previous attributes are deleted, otherwise they are left untouched.

WARNING: if you rely on ID’s then you will have to set the id yourself. At this point the element does not belong to a twig yet, so the ID attribute is not known so it won’t be stored in the ID list.

A content of ’CW#EMPTY’ creates an empty element;

namespace ($optional_prefix) Return the URI of the namespace that CW$optional_prefix or the element name belongs to. If the name doesn’t belong to any namespace, CWundef is returned.
local_name Return the local name (without the prefix) for the element
ns_prefix Return the namespace prefix for the element
current_ns_prefixes Return a list of namespace prefixes valid for the element. The order of the prefixes in the list has no meaning. If the default namespace is currently bound, ’’ appears in the list.
inherit_att ($att, CW@optional_tag_list) Return the value of an attribute inherited from parent tags. The value returned is found by looking for the attribute in the element then in turn in each of its ancestors. If the CW@optional_tag_list is supplied only those ancestors whose tag is in the list will be checked.
all_children_are ($optional_condition) return 1 if all children of the element pass the CW$optional_condition, 0 otherwise
level ($optional_condition) Return the depth of the element in the twig (root is 0). If CW$optional_condition is given then only ancestors that match the condition are counted.

WARNING: in a tree created using the CWtwig_roots option this will not return the level in the document tree, level 0 will be the document root, level 1 will be the CWtwig_roots elements. During the parsing (in a CWtwig_handler) you can use the CWdepth method on the twig object to get the real parsing depth.

in ($potential_parent) Return true if the element is in the potential_parent (CW$potential_parent is an element)
in_context ($cond, CW$optional_level) Return true if the element is included in an element which passes CW$cond optionally within CW$optional_level levels. The returned value is the including element.
pcdata Return the text of a CWPCDATA element or CWundef if the element is not CWPCDATA.
pcdata_xml_string Return the text of a CWPCDATA element or undef if the element is not CWPCDATA. The text is XML-escaped (’&’ and ’<’ are replaced by ’&’ and ’<’)
set_pcdata ($text) Set the text of a CWPCDATA element. This method does not check that the element is indeed a CWPCDATA so usually you should use CWset_text instead.
append_pcdata ($text) Add the text at the end of a CWPCDATA element.
is_cdata Return 1 if the element is a CWCDATA element, returns 0 otherwise.
is_text Return 1 if the element is a CWCDATA or CWPCDATA element, returns 0 otherwise.
cdata Return the text of a CWCDATA element or CWundef if the element is not CWCDATA.
cdata_string Return the XML string of a CWCDATA element, including the opening and closing markers.
set_cdata ($text) Set the text of a CWCDATA element.
append_cdata ($text) Add the text at the end of a CWCDATA element.
remove_cdata Turns all CWCDATA sections in the element into regular CWPCDATA elements. This is useful when converting XML to HTML, as browsers do not support CDATA sections.
extra_data Return the extra_data (comments and PI’s) attached to an element
set_extra_data ($extra_data) Set the extra_data (comments and PI’s) attached to an element
append_extra_data ($extra_data) Append extra_data to the existing extra_data before the element (if no previous extra_data exists then it is created)
set_asis Set a property of the element that causes it to be output without being XML escaped by the print functions: if it contains CWa < b it will be output as such and not as CWa < b. This can be useful to create text elements that will be output as markup. Note that all CWPCDATA descendants of the element are also marked as having the property (they are the ones that are actually impacted by the change).

If the element is a CWCDATA element it will also be output asis, without the CWCDATA markers. The same goes for any CWCDATA descendant of the element

set_not_asis Unsets the CWasis property for the element and its text descendants.
is_asis Return the CWasis property status of the element ( 1 or CWundef)
closed Return true if the element has been closed. Might be useful if you are somewhere in the tree, during the parse, and have no idea whether a parent element is completely loaded or not.
get_type Return the type of the element: ’CW#ELT’ for real elements, or ’CW#PCDATA’, ’CW#CDATA’, ’CW#COMMENT’, ’CW#ENT’, ’CW#PI
is_elt Return the tag if the element is a real element, or 0 if it is CWPCDATA, CWCDATA...
contains_only_text Return 1 if the element does not contain any other real element
contains_only ($exp) Return the list of children if all children of the element match the expression CW$exp



  if( $para->contains_only( tt)) { ... }



contains_a_single ($exp) If the element contains a single child that matches the expression CW$exp returns that element. Otherwise returns 0.
is_field same as CWcontains_only_text
is_pcdata Return 1 if the element is a CWPCDATA element, returns 0 otherwise.
is_ent Return 1 if the element is an entity (an unexpanded entity) element, return 0 otherwise.
is_empty Return 1 if the element is empty, 0 otherwise
set_empty Flags the element as empty. No further check is made, so if the element is actually not empty the output will be messed. The only effect of this method is that the output will be CW<tag att="value""/>.
set_not_empty Flags the element as not empty. if it is actually empty then the element will be output as CW<tag att="value""></tag>
is_pi Return 1 if the element is a processing instruction (CW#PI) element, return 0 otherwise.
target Return the target of a processing instruction
set_target ($target) Set the target of a processing instruction
data Return the data part of a processing instruction
set_data ($data) Set the data of a processing instruction
set_pi ($target, CW$data) Set the target and data of a processing instruction
pi_string Return the string form of a processing instruction (CW<?target data?>)
is_comment Return 1 if the element is a comment (CW#COMMENT) element, return 0 otherwise.
set_comment ($comment_text) Set the text for a comment
comment Return the content of a comment (just the text, not the CW<!-- and CW-->)
comment_string Return the XML string for a comment (CW<!-- comment -->)
set_ent ($entity) Set an (non-expanded) entity (CW#ENT). CW$entity) is the entity text (CW&ent;)
ent Return the entity for an entity (CW#ENT) element (CW&ent;)
ent_name Return the entity name for an entity (CW#ENT) element (CWent)
ent_string Return the entity, either expanded if the expanded version is available, or non-expanded (CW&ent;) otherwise
child ($offset, CW$optional_condition) Return the CW$offset-th child of the element, optionally the CW$offset-th child that matches CW$optional_condition. The children are treated as a list, so CW$elt->child( 0) is the first child, while CW$elt->child( -1) is the last child.
child_text ($offset, CW$optional_condition) Return the text of a child or CWundef if the sibling does not exist. Arguments are the same as child.
last_child ($optional_condition) Return the last child of the element, or the last child matching CW$optional_condition (ie the last of the element children matching the condition).
last_child_text ($optional_condition) Same as CWfirst_child_text but for the last child.
sibling ($offset, CW$optional_condition) Return the next or previous CW$offset-th sibling of the element, or the CW$offset-th one matching CW$optional_condition. If CW$offset is negative then a previous sibling is returned, if CW$offset is positive then a next sibling is returned. CW$offset=0 returns the element if there is no condition or if the element matches the condition>, CWundef otherwise.
sibling_text ($offset, CW$optional_condition) Return the text of a sibling or CWundef if the sibling does not exist. Arguments are the same as CWsibling.
prev_siblings ($optional_condition) Return the list of previous siblings (optionally matching CW$optional_condition) for the element. The elements are ordered in document order.
next_siblings ($optional_condition) Return the list of siblings (optionally matching CW$optional_condition) following the element. The elements are ordered in document order.
pos ($optional_condition) Return the position of the element in the children list. The first child has a position of 1 (as in XPath).

If the CW$optional_condition is given then only siblings that match the condition are counted. If the element itself does not match the condition then 0 is returned.

atts Return a hash ref containing the element attributes
set_atts ({ att1=>$att1_val, att2=> CW$att2_val... }) Set the element attributes with the hash ref supplied as the argument. The previous attributes are lost (ie the attributes set by CWset_atts replace all of the attributes of the element).

You can also pass a list instead of a hashref: CW$elt->set_atts( att1 => val1,...)

del_atts Deletes all the element attributes.
att_nb Return the number of attributes for the element
has_atts Return true if the element has attributes (in fact return the number of attributes, thus being an alias to CWatt_nb
has_no_atts Return true if the element has no attributes, false (0) otherwise
att_names return a list of the attribute names for the element
att_xml_string ($att, CW$options) Return the attribute value, where ’&’, ’<’ and quote (" or the value of the quote option at twig creation) are XML-escaped.

The options are passed as a hashref, setting CWescape_gt to a true value will also escape ’>’ ($elt( ’myatt’, { escape_gt => 1 });

set_id ($id) Set the CWid attribute of the element to the value. See CWelt_id to change the id attribute name
id Gets the id attribute value
del_id ($id) Deletes the CWid attribute of the element and remove it from the id list for the document
class Return the CWclass attribute for the element (methods on the CWclass attribute are quite convenient when dealing with XHTML, or plain XML that will eventually be displayed using CSS)
set_class ($class) Set the CWclass attribute for the element to CW$class
add_to_class ($class) Add CW$class to the element CWclass attribute: the new class is added only if it is not already present. Note that classes are sorted alphabetically, so the CWclass attribute can be changed even if the class is already there
att_to_class ($att) Set the CWclass attribute to the value of attribute CW$att
add_att_to_class ($att) Add the value of attribute CW$att to the CWclass attribute of the element
move_att_to_class ($att) Add the value of attribute CW$att to the CWclass attribute of the element and delete the attribute
tag_to_class Set the CWclass attribute of the element to the element tag
add_tag_to_class Add the element tag to its CWclass attribute
set_tag_class ($new_tag) Add the element tag to its CWclass attribute and sets the tag to CW$new_tag
in_class ($class) Return true (CW1) if the element is in the class CW$class (if CW$class is one of the tokens in the element CWclass attribute)
tag_to_span Change the element tag tp CWspan and set its class to the old tag
tag_to_div Change the element tag tp CWdiv and set its class to the old tag
DESTROY Frees the element from memory.
start_tag Return the string for the start tag for the element, including the CW/> at the end of an empty element tag
end_tag Return the string for the end tag of an element. For an empty element, this returns the empty string (’’).
xml_string CW@optional_options Equivalent to CW$elt->sprint( 1), returns the string for the entire element, excluding the element’s tags (but nested element tags are present)

The ’CWno_recurse’ option will only return the text of the element, not of any included sub-elements (same as CWxml_text_only).

inner_xml Another synonym for xml_string
outer_xml Another synonym for sprint
xml_text Return the text of the element, encoded (and processed by the current CWoutput_filter or CWoutput_encoding options, without any tag.
xml_text_only Same as CWxml_text except that the text returned doesn’t include the text of sub-elements.
set_pretty_print ($style) Set the pretty print method, amongst ’CWnone’ (default), ’CWnsgmls’, ’CWnice’, ’CWindented’, ’CWrecord’ and ’CWrecord_c

pretty_print styles:
none the default, no CW\n is used
nsgmls nsgmls style, with CW\n added within tags
nice adds CW\n wherever possible (NOT SAFE, can lead to invalid XML)
indented same as CWnice plus indents elements (NOT SAFE, can lead to invalid XML)
record table-oriented pretty print, one field per line
record_c table-oriented pretty print, more compact than CWrecord, one record per line

set_empty_tag_style ($style) Set the method to output empty tags, amongst ’CWnormal’ (default), ’CWhtml’, and ’CWexpand’,

CWnormal outputs an empty tag ’CW<tag/>’, CWhtml adds a space ’CW<tag />’ for elements that can be empty in XHTML and CWexpand outputs ’CW<tag></tag>

set_remove_cdata ($flag) set (or unset) the flag that forces the twig to output CDATA sections as regular (escaped) PCDATA
set_indent ($string) Set the indentation for the indented pretty print style (default is 2 spaces)
set_quote ($quote) Set the quotes used for attributes. can be ’CWdouble’ (default) or ’CWsingle
cmp ($elt)


  Compare the order of the 2 elements in a twig.

  C<$a> is the <A>..</A> element, C<$b> is the <B>...</B> element

  document                        $a->cmp( $b)
  <A> ... </A> ... <B>  ... </B>     -1
  <A> ... <B>  ... </B> ... </A>     -1
  <B> ... </B> ... <A>  ... </A>      1
  <B> ... <A>  ... </A> ... </B>      1
   $a == $b                           0
   $a and $b not in the same tree   undef



before ($elt) Return 1 if CW$elt starts before the element, 0 otherwise. If the 2 elements are not in the same twig then return CWundef.



    if( $a->cmp( $b) == -1) { return 1; } else { return 0; }



after ($elt) Return 1 if CW$elt starts after the element, 0 otherwise. If the 2 elements are not in the same twig then return CWundef.



    if( $a->cmp( $b) == -1) { return 1; } else { return 0; }



other comparison methods
lt
le
gt
ge
path Return the element context in a form similar to XPath’s short form: ’CW/root/tag1/../tag
xpath Return a unique XPath expression that can be used to find the element again.

It looks like CW/doc/sect[3]/title: unique elements do not have an index, the others do.

private methods Low-level methods on the twig:
set_parent ($parent)
set_first_child ($first_child)
set_last_child ($last_child)
set_prev_sibling ($prev_sibling)
set_next_sibling ($next_sibling)
set_twig_current
del_twig_current
twig_current
flush This method should NOT be used, always flush the twig, not an element.
contains_text

Those methods should not be used, unless of course you find some creative and interesting, not to mention useful, ways to do it.

    cond

Most of the navigation functions accept a condition as an optional argument The first element (or all elements for CWchildren or CWancestors ) that passes the condition is returned.

The condition is a single step of an XPath expression using the XPath subset defined by CWget_xpath. Additional conditions are:

The condition can be
#ELT return a real element (not a PCDATA, CDATA, comment or pi element)
#TEXT return a PCDATA or CDATA element
regular expression return an element whose tag matches the regexp. The regexp has to be created with CWqr// (hence this is available only on perl 5.005 and above)
code reference applies the code, passing the current element as argument, if the code returns true then the element is returned, if it returns false then the code is applied to the next candidate.

    XML::Twig::XPath

XML::Twig implements a subset of XPath through the CWget_xpath method.

If you want to use the whole XPath power, then you can use CWXML::Twig::XPath instead. In this case CWXML::Twig uses CWXML::XPath to execute XPath queries. You will of course need CWXML::XPath installed to be able to use CWXML::Twig::XPath.

See XML::XPath for more information.

The methods you can use are:
findnodes ($path) return a list of nodes found by CW$path.
findnodes_as_string ($path) return the nodes found reproduced as XML. The result is not guaranteed to be valid XML though.
findvalue ($path) return the concatenation of the text content of the result nodes
In order for CWXML::XPath to be used as the XPath engine the following methods are included in CWXML::Twig:

in XML::Twig
getRootNode
getParentNode
getChildNodes
in XML::Twig::Elt
string_value
toString
getName
getRootNode
getNextSibling
getPreviousSibling
isElementNode
isTextNode
isPI
isPINode
isProcessingInstructionNode
isComment
isCommentNode
getTarget
getChildNodes
getElementById

    XML::Twig::XPath::Elt

The methods you can use are the same as on CWXML::Twig::XPath elements:
findnodes ($path) return a list of nodes found by CW$path.
findnodes_as_string ($path) return the nodes found reproduced as XML. The result is not guaranteed to be valid XML though.
findvalue ($path) return the concatenation of the text content of the result nodes

    XML::Twig::Entity_list

new Create an entity list.
add ($ent) Add an entity to an entity list.
add_new_ent ($name, CW$val, CW$sysid, CW$pubid, CW$ndata, CW$param) Create a new entity and add it to the entity list
delete ($ent or CW$tag). Delete an entity (defined by its name or by the Entity object) from the list.
print ($optional_filehandle) Print the entity list.
list Return the list as an array

    XML::Twig::Entity

new ($name, CW$val, CW$sysid, CW$pubid, CW$ndata, CW$param) Same arguments as the Entity handler for XML::Parser.
print ($optional_filehandle) Print an entity declaration.
name Return the name of the entity
val Return the value of the entity
sysid Return the system id for the entity (for NDATA entities)
pubid Return the public id for the entity (for NDATA entities)
ndata Return true if the entity is an NDATA entity
param Return true if the entity is a parameter entity
text Return the entity declaration text.

EXAMPLES

Additional examples (and a complete tutorial) can be found on the XML::Twig Page<http://www.xmltwig.com/xmltwig/>

To figure out what flush does call the following script with an XML file and an element name as arguments



  use XML::Twig;

  my ($file, $elt)= @ARGV;
  my $t= XML::Twig->new( twig_handlers =>
      { $elt => sub {$_[0]->flush; print "\n[flushed here]\n";} });
  $t->parsefile( $file, ErrorContext => 2);
  $t->flush;
  print "\n";



NOTES

    Subclassing XML::Twig

Useful methods:
elt_class In order to subclass CWXML::Twig you will probably need to subclass also CWXML::Twig::Elt. Use the CWelt_class option when you create the CWXML::Twig object to get the elements created in a different class (which should be a subclass of CWXML::Twig::Elt.
add_options If you inherit CWXML::Twig new method but want to add more options to it you can use this method to prevent XML::Twig to issue warnings for those additional options.

    DTD Handling

There are 3 possibilities here. They are:
No DTD No doctype, no DTD information, no entity information, the world is simple...
Internal DTD The XML document includes an internal DTD, and maybe entity declarations.

If you use the load_DTD option when creating the twig the DTD information and the entity declarations can be accessed.

The DTD and the entity declarations will be CWflush’ed (or CWprint’ed) either as is (if they have not been modified) or as reconstructed (poorly, comments are lost, order is not kept, due to it’s content this DTD should not be viewed by anyone) if they have been modified. You can also modify them directly by changing the CW$twig->{twig_doctype}->{internal} field (straight from XML::Parser, see the CWDoctype handler doc)

External DTD The XML document includes a reference to an external DTD, and maybe entity declarations.

If you use the CWload_DTD when creating the twig the DTD information and the entity declarations can be accessed. The entity declarations will be CWflush’ed (or CWprint’ed) either as is (if they have not been modified) or as reconstructed (badly, comments are lost, order is not kept).

You can change the doctype through the CW$twig->set_doctype method and print the dtd through the CW$twig->dtd_text or CW$twig->dtd_print
methods.

If you need to modify the entity list this is probably the easiest way to do it.

    Flush

If you set handlers and use CWflush, do not forget to flush the twig one last time AFTER the parsing, or you might be missing the end of the document.

Remember that element handlers are called when the element is CLOSED, so if you have handlers for nested elements the inner handlers will be called first. It makes it for example trickier than it would seem to number nested clauses.

BUGS

entity handling Due to XML::Parser behaviour, non-base entities in attribute values disappear: CWatt="val&ent;" will be turned into CWatt => val, unless you use the CWkeep_encoding argument to CWXML::Twig->new
DTD handling The DTD handling methods are quite bugged. No one uses them and it seems very difficult to get them to work in all cases, including with several slightly incompatible versions of XML::Parser and of libexpat.

Basically you can read the DTD, output it back properly, and update entities, but not much more.

So use XML::Twig with standalone documents, or with documents refering to an external DTD, but don’t expect it to properly parse and even output back the DTD.

memory leak If you use a lot of twigs you might find that you leak quite a lot of memory (about 2Ks per twig). You can use the CWdispose method to free that memory after you are done.

If you create elements the same thing might happen, use the CWdelete method to get rid of them.

Alternatively installing the CWScalar::Util (or CWWeakRef) module on a version of Perl that supports it (>5.6.0) will get rid of the memory leaks automagically.

ID list The ID list is NOT updated when elements are cut or deleted.
change_gi This method will not function properly if you do:



     $twig->change_gi( $old1, $new);
     $twig->change_gi( $old2, $new);
     $twig->change_gi( $new, $even_newer);



sanity check on XML::Parser method calls XML::Twig should really prevent calls to some XML::Parser methods, especially the CWsetHandlers method.
pretty printing Pretty printing (at least using the ’CWindented’ style) is hard to get right! Only elements that belong to the document will be properly indented. Printing elements that do not belong to the twig makes it impossible for XML::Twig to figure out their depth, and thus their indentation level.

Also there is an unavoidable bug when using CWflush and pretty printing for elements with mixed content that start with an embedded element:



  <elt><b>b</b>toto<b>bold</b></elt>

  will be output as

  <elt>
    <b>b</b>toto<b>bold</b></elt>



if you flush the twig when you find the CW<b> element

Globals

These are the things that can mess up calling code, especially if threaded. They might also cause problem under mod_perl.
Exported constants Whether you want them or not you get them! These are subroutines to use as constant when creating or testing elements



  PCDATA  return #PCDATA
  CDATA   return #CDATA
  PI      return #PI, I had the choice between PROC and PI :--(



Module scoped values: constants these should cause no trouble:



  %base_ent= ( > => >,
               < => <,
               & => &,
               "" => ',
               " => ",
             );
  CDATA_START   = "<![CDATA[";
  CDATA_END     = "]]>";
  PI_START      = "<?";
  PI_END        = "?>";
  COMMENT_START = "<!--";
  COMMENT_END   = "-->";



pretty print styles



  ( $NSGMLS, $NICE, $INDENTED, $INDENTED_C, $WRAPPED, $RECORD1, $RECORD2)= (1..7);



empty tag output style



  ( $HTML, $EXPAND)= (1..2);



Module scoped values: might be changed Most of these deal with pretty printing, so the worst that can happen is probably that XML output does not look right, but is still valid and processed identically by XML processors.

CW$empty_tag_style can mess up HTML bowsers though and changing CW$ID would most likely create problems.



  $pretty=0;           # pretty print style
  $quote=";          # quote for attributes
  $INDENT=   ;       # indent for indented pretty print
  $empty_tag_style= 0; # how to display empty tags
  $ID                  # attribute used as an id (id by default)



Module scoped values: definitely changed These 2 variables are used to replace tags by an index, thus saving some space when creating a twig. If they really cause you too much trouble, let me know, it is probably possible to create either a switch or at least a version of XML::Twig that does not perform this optimization.



  %gi2index;     # tag => index
  @index2gi;     # list of tags



If you need to manipulate all those values, you can use the following methods on the XML::Twig object:
global_state Return a hashref with all the global variables used by XML::Twig

The hash has the following fields: CWpretty, CWquote, CWindent, CWempty_tag_style, CWkeep_encoding, CWexpand_external_entities, CWoutput_filter, CWoutput_text_filter, CWkeep_atts_order

set_global_state ($state) Set the global state, CW$state is a hashref
save_global_state Save the current global state
restore_global_state Restore the previously saved (using CWLsave_global_state> state

TODO

SAX handlers Allowing XML::Twig to work on top of any SAX parser
multiple twigs are not well supported A number of twig features are just global at the moment. These include the ID list and the tag pool (if you use CWchange_gi then you change the tag for ALL twigs).

A future version will try to support this while trying not to be to hard on performance (at least when a single twig is used!).

AUTHOR

Michel Rodriguez <mirod@xmltwig.com>

LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Bug reports should be sent using: RT <http://rt.cpan.org/NoAuth/Bugs.html?Dist=XML-Twig>

Comments can be sent to mirod@xmltwig.com

The XML::Twig page is at <http://www.xmltwig.com/xmltwig/> It includes the development version of the module, a slightly better version of the documentation, examples, a tutorial and a: Processing XML efficiently with Perl and XML::Twig: <http://www.xmltwig.com/xmltwig/tutorial/index.html>

SEE ALSO

Complete docs, including a tutorial, examples, an easier to use HTML version of the docs, a quick reference card and a FAQ are available at <http://www.xmltwig.com/xmltwig/>

git repository at <http://github.com/mirod/xmltwig>

XML::Parser, XML::Parser::Expat, XML::XPath, Encode, Text::Iconv, Scalar::Utils

    Alternative Modules

XML::Twig is not the only XML::Processing module available on CPAN (far from it!).

The main alternative I would recommend is XML::LibXML.

Here is a quick comparison of the 2 modules:

XML::LibXML, actually CWlibxml2 on which it is based, sticks to the standards, and implements a good number of them in a rather strict way: XML, XPath, DOM, RelaxNG, I must be forgetting a couple (XInclude?). It is fast and rather frugal memory-wise.

XML::Twig is older: when I started writing it XML::Parser/expat was the only game in town. It implements XML and that’s about it (plus a subset of XPath, and you can use XML::Twig::XPath if you have XML::XPathEngine installed for full support). It is slower and requires more memory for a full tree than XML::LibXML. On the plus side (yes, there is a plus side!) it lets you process a big document in chunks, and thus let you tackle documents that couldn’t be loaded in memory by XML::LibXML, and it offers a lot (and I mean a LOT!) of higher-level methods, for everything, from adding structure to low-level XML, to shortcuts for XHTML conversions and more. It also DWIMs quite a bit, getting comments and non-significant whitespaces out of the way but preserving them in the output for example. As it does not stick to the DOM, is also usually leads to shorter code than in XML::LibXML.

Beyond the pure features of the 2 modules, XML::LibXML seems to be preferred by XML-purists, while XML::Twig seems to be more used by Perl Hackers who have to deal with XML. As you have noted, XML::Twig also comes with quite a lot of docs, but I am sure if you ask for help about XML::LibXML here or on Perlmonks you will get answers.

Note that it is actually quite hard for me to compare the 2 modules: on one hand I know XML::Twig inside-out and I can get it to do pretty much anything I need to (or I improve it ;--), while I have a very basic knowledge of XML::LibXML. So feature-wise, I’d rather use XML::Twig ;--). On the other hand, I am painfully aware of some of the deficiencies, potential bugs and plain ugly code that lurk in XML::Twig, even though you are unlikely to be affected by them (unless for example you need to change the DTD of a document programatically), while I haven’t looked much into XML::LibXML so it still looks shinny and clean to me.

That said, if you need to process a document that is too big to fit memory and XML::Twig is too slow for you, my reluctant advice would be to use bare XML::Parser. It won’t be as easy to use as XML::Twig: basically with XML::Twig you trade some speed (depending on what you do from a factor 3 to... none) for ease-of-use, but it will be easier IMHO than using SAX (albeit not standard), and at this point a LOT faster (see the last test in <http://www.xmltwig.com/article/simple_benchmark/>).

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