Tagset(3)

NAME
HTML::Tagset - data tables useful in parsing HTML

SYNOPSIS
  use HTML::Tagset;
  # Then use any of the items in the HTML::Tagset package
  #  as need arises

DESCRIPTION
This module contains several data tables useful in various kinds of HTML parsing operations.

Note that all tag names used are lowercase.

In the following documentation, a "hashset" is a hash being used as a set -- the hash conveys that its keys are there, and the actual values associated with the keys are not significant. (But what values are there, are always true.) This hashset has as values the tag-names (GIs) of elements that cannot have content. (For example, "base", "br", "hr".) So `$HTML::Tagset::emptyElement{'hr'}' exists and is true. `$HTML::Tagset::emptyElement{'dl'}' does not exist, and so is not true. This hashset lists tag-names for elements that can have content, but whose end-tags are generally, "safely", omissible. Example: `$HTML::Tagset::emptyElement{'li'}' exists and is true. Values in this hash are tagnames for elements that might contain links, and the value for each is a reference to an array of the names of attributes whose values can be links. This hash (not hashset) lists what attributes of what elements can be printed without showing the value (for example, the "noshade" attribute of "hr" elements). For elements with only one such attribute, its value is simply that attribute name. For elements with many such attributes, the value is a reference to a hashset containing all such attributes. This hashset contains all phrasal-level elements. This hashset contains all phrasal-level elements that be content of a P element, for a strict model of HTML. This hashset contains all elements that elements that should be present only in the 'head' element of an HTML document. This hashset contains all elements that can contain "li" elements. This hashset contains all elements that are to be found only in/under a "table" element. This hashset contains all elements that are to be found only in/under a "form" element. This hashset contains all elements that are to be found only in/under the "body" element of an HTML document. This hashset includes all elements that I notice can fall either in the head or in the body. This hashset lists all known HTML elements. This hashset lists elements that might have ignorable whitespace as children or siblings. This array has a meaning that I have only seen a need for in `HTML::TreeBuilder', but I include it here on the off chance that someone might find it of use:

When we see a "<p>" token, we go lookup up the lineage for a p element we might have to minimize. At first sight, we might say that if there's a p anywhere in the lineage of this new p, it should be closed. But that's wrong. Consider this document:

  <html>
    <head>
      <title>foo</title>
    </head>
    <body>
      <p>foo
        <table>
          <tr>
            <td>
               foo
               <p>bar
            </td>
          </tr>
        </table>
      </p>
    </body>
  </html>
The second p is quite legally inside a much higher p.

My formalization of the reason why this is legal, but this:

  <p>foo<p>bar</p></p>
isn't, is that something about the table constitutes a "barrier" to the application of the rule about what p must minimize.

So `@HTML::Tagset::p_closure_barriers' is the list of all such barrier-tags. This hashset includes all elements whose content is CDATA.

CAVEATS
You may find it useful to alter the behavior of modules (like `HTML::Element' or `HTML::TreeBuilder') that use `HTML::Tagset''s data tables by altering the data tables themselves. You are welcome to try, but be careful; and be aware that different modules may or may react differently to the data tables being changed.

Note that it may be inappropriate to use these tables for producing HTML -- for example, `%isHeadOrBodyElement' lists the tagnames for all elements that can appear either in the head or in the body, such as "script". That doesn't mean that I am saying your code that produces HTML should feel free to put script elements in either place! If you are producing programs that spit out HTML, you should be intimately familiar with the DTDs for HTML or XHTML (available at `http://www.w3.org/'), and you should slavishly obey them, not the data tables in this document.

SEE ALSO
the HTML::Element manpage, the HTML::TreeBuilder manpage, the HTML::LinkExtor manpage

COPYRIGHT
Copyright 1995-2000 Gisle Aas; copyright 2000 Sean M. Burke.

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

AUTHOR
Current maintainer: Sean M. Burke, <sburke@cpan.org>

Most of the code/data in this module was adapted from code written by Gisle Aas <gisle@aas.no> for `HTML::Element', `HTML::TreeBuilder', and `HTML::LinkExtor'.