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Benjamin Holzman


XML::Generator - Perl extension for generating XML


   use XML::Generator;
   my $xml = XML::Generator->new(escape => 'always',
                                 pretty => 2,
                                 conformance => 'strict');

   print $xml->foo($xml->bar({ baz => 3 }, $xml->bam),
                   $xml->bar([ 'qux' ], "Hey there, world"));
   # The above would yield:
     <bar baz="3">
       <bam />
     <qux:bar>Hey there, world</qux:bar>


In general, once you have an XML::Generator object, you then simply call methods on that object named for each XML tag you wish to generate. Say you want to generate this XML:


Here's a snippet of code that does the job, complete with pretty printing:

   use XML::Generator;
   my $gen = XML::Generator->new(escape => 'always', pretty => 2);
   print $gen->person(

The only problem with this is if you want to use a tag name that Perl's lexer won't understand as a method name, such as "shoe-size". Fortunately, since you can always call methods as variable names, there's a simple work-around:

   my $shoe_size = "shoe-size";
   $xml = $gen->$shoe_size("12 1/2");

Which correctly generates:

   <shoe-size>12 1/2</shoe-size>

You can use a hash ref as the first parameter if the tag should include atributes. An array ref can be supplied as the first argument to indicate a namespace for the element and the attributes (the elements of the array are concatenated with ':'). Under strict conformance, however, you are only allowed one namespace component.

If you want to specify a namespace as well as attributes, you can make the second argument a hash ref. If you do it the other way around, the array ref will simply get stringified and included as part of the content of the tag. If an XML::Generator object has a namespace set, and a namespace is also supplied to the tag, the supplied namespace overrides the default.

Here's an example to show how the attribute and namespace parameters work:

   $xml = $gen->account({ type => 'checking', id => '34758'},
            $gen->open(['transaction'], 2000),
            $gen->deposit(['transaction'], { date => '1999.04.03'}, 1500)

This generates:

   <account type="checking" id="34578">
     <transaction:deposit transaction:date="1999.04.03">1500</transaction:deposit>


XML::Generator->new(option => 'value', option => 'value');

The following options are available:


The value of this option is used as the global default namespace. For example,

   my $html = XML::Generator->new(namespace => 'HTML');
   print $html->font({ face => 'Arial' }, "Hello, there");

would yield

   <HTML:font HTML:face="Arial">Hello, there</HTML:font>

See HTML::Generator for routines specific to HTML generation.


The contents and the values of each attribute have any illegal XML characters escaped if this option is supplied. If the value is 'always', then &, < and > (and " within attribute values) will be converted into the corresponding XML entity. If the value is any other true value, then the escaping will be turned off character-by-character if the character in question is preceded by a backslash, or for the entire string if it is supplied as a scalar reference. So, for example,

   my $a = XML::Generator->new(escape => 'always');
   my $b = XML::Generator->new(escape => 'true');
   print $a->foo('<', $b->bar('3 \> 4', \" && 6 < 5"), '\&', '>');

would yield

   <foo>&lt;<bar>3 > 4 && 6 < 5</bar>\&amp;&gt;</foo>


To have nice pretty printing of the output XML (great for config files that you might also want to edit by hand), pass an integer for the number of spaces per level of indenting, eg.

   my $gen = XML::Generator->new(pretty => 2);
   print $gen->foo($gen->bar('baz'),
                   $gen->qux({ tricky => 'no'}, 'quux'));

would yield

     <qux tricky="no">quux</qux>

Pretty printing does not apply to CDATA sections or Processing Instructions.


If the value of this option is 'strict', a number of syntactic checks are performed to ensure that generated XML conforms to the formal XML specification. In addition, since entity names beginning with 'xml' are reserved by the W3C, inclusion of this option enables several special tag names: xmlpi, xmlcmnt, xmldecl, xmldtd, xmlcdata, and xml to allow generation of processing instructions, comments, XML declarations, DTD's, character data sections and "final" XML documents, respectively.

See "XML CONFORMANCE" and "SPECIAL TAGS" for more information.


There are 5 possible values for this option:

   self    -  create empty tags as <tag />  (default)
   compact -  create empty tags as <tag/>
   close   -  close empty tags as <tag></tag>
   ignore  -  don't do anything (non-compliant!)
   args    -  use count of arguments to decide between <x /> and <x></x>

Many web browsers like the 'self' form, but any one of the forms besides 'ignore' is acceptable under the XML standard.

'ignore' is intended for subclasses that deal with HTML and other SGML subsets which allow atomic tags. It is an error to specify both 'conformance' => 'strict' and 'empty' => 'ignore'.

'args' will produce <x /> if there are no arguments at all, or if there is just a single undef argument, and <x></x> otherwise.


When the 'conformance' => 'strict' option is supplied, a number of syntactic checks are enabled. All entity and attribute names are checked to conform to the XML specification, which states that they must begin with either an alphabetic character or an underscore and may then consist of any number of alphanumerics, underscores, periods or hyphens. Alphabetic and alphanumeric are interpreted according to the current locale if 'use locale' is in effect and according to the Unicode standard for Perl versions >= 5.6. Furthermore, entity or attribute names are not allowed to begin with 'xml' (in any case), although a number of special tags beginning with 'xml' are allowed (see "SPECIAL TAGS").

In addition, only one namespace component will be allowed when strict conformance is in effect, and attribute names can be given a specific namespace, which will override both the default namespace and the tag- specific namespace. For example,

   my $gen = XML::Generator->new(conformance => 'strict',
                                 namespace   => 'foo');
   my $xml = $gen->bar({ a => 1 },
               $gen->baz(['bam'], { b => 2, 'name:c' => 3 })

will generate:

   <foo:bar foo:a="1"><bam:baz bam:b="2" name:c="3" /></foo:bar>


The following special tags are available when running under strict conformance (otherwise they don't act special):


Processing instruction; first argument is target, remaining arguments are attribute, value pairs. Attribute names are syntax checked, values are escaped.


Comment. Arguments are concatenated and placed inside <!-- ... --> comment delimiters. Any occurences of '--' in the concatenated arguments are converted to '-&#45;'


Declaration. This can be used to specify the version, encoding, and other XML-related declarations (i.e., anything inside the <?xml?> tag).


DTD <!DOCTYPE> tag creation. The format of this method is different from others. Since DTD's are global and cannot contain namespace information, the first argument arrayref is concatenated together to form the DTD:

   print $xml->xmldtd([ 'html', 'PUBLIC', $xhtml_w3c, $xhtml_dtd ])

This would produce the following declaration:

   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

Assuming that $xhtml_w3c and $xhtml_dtd had the correct values. For shortcuts to <!DOCTYPE> generation, see the HTML::Generator module. Note that you can also specify a DTD on creation using the new() method's dtd option.


Character data section; arguments are concatenated and placed inside <![CDATA[ ... ]]> character data section delimiters. Any occurences of ']]>' in the concatenated arguments are converted to ']]&gt;'.


"Final" XML document. Must be called with one and exactly one XML::Generator-produced XML document. Any combination of XML::Generator-produced XML comments or processing instructions may also be supplied as arguments. Prepends an XML declaration, and re-blesses the argument into a "final" class that can't be embedded.


For an example of how to subclass XML::Generator, see Nathan Wiger's HTML::Generator module.

At times, you may find it desireable to subclass XML::Generator. For example, you might want to provide a more application-specific interface to the XML generation routines provided. Perhaps you have a custom database application and would really like to say:

   my $dbxml = new XML::Generator::MyDatabaseApp;
   print $dbxml->xml($dbxml->custom_tag_handler(@data));

Here, custom_tag_handler() may be a method that builds a recursive XML structure based on the contents of @data. In fact, it may even be named for a tag you want generated, such as authors(), whose behavior changes based on the contents (perhaps creating recursive definitions in the case of multiple elements).

Creating a subclass of XML::Generator is actually relatively straightforward, there are just three things you have to remember:

   1. All of the useful utilities are in XML::Generator::util.

   2. To construct a tag you simply have to call SUPER::tagname,
      where "tagname" is the name of your tag.

   3. You must fully-qualify the methods in XML::Generator::util.

So, let's assume that we want to provide a custom HTML table() method:

   package XML::Generator::CustomHTML;
   use base 'XML::Generator';

   sub table {
       my $self = shift;
       # parse our args to get namespace and attribute info
       my($namespace, $attr, @content) =

       # check for strict conformance
       if ( $self->XML::Generator::util::config('conformance') eq 'strict' ) {
          # ... special checks ...

       # ... special formatting magic happens ...

       # construct our custom tags
       return $self->SUPER::table($attr, $self->tr($self->td(@content)));

That's pretty much all there is to it. We have to explicitly call SUPER::table() since we're inside the class's table() method. The others can simply be called directly, assuming that we don't have a tr() in the current package.

If you want to explicitly create a specific tag by name, or just want a faster approach than AUTOLOAD provides, you can use the tag() method directly. So, we could replace that last line above with:

       # construct our custom tags 
       return $self->XML::Generator::util::tag('table', $attr, ...);

Here, we must explicitly call tag() with the tag name itself as its first argument so it knows what to generate. These are the methods that you might find useful:


This parses the argument list and returns the namespace (arrayref), attributes (hashref), and remaining content (array), in that order.


This does the work of generating the appropriate tag. The first argument must be the name of the tag to generate.


This retrieves options as set via the new() method.


This escapes any illegal XML characters.

Remember that all of these methods must be fully-qualified with the XML::Generator::util package name. This is because AUTOLOAD is used by the main XML::Generator package to create tags. Simply calling parse_args() will result in a set of XML tags called <parse_args>.

Finally, remember that since you are subclassing XML::Generator, you do not need to provide your own new() method. The one from XML::Generator is designed to allow you to properly subclass it.


Benjamin Holzman <bholzman@earthlink.net>

Original author and maintainer

Bron Gondwana <perlcode@brong.net>

First modular version

Nathan Wiger <nate@nateware.com>

Modular rewrite to enable subclassing




The XML::Writer module


The XML::Handler::YAWriter module


The HTML::Generator module