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Pod::Tree::HTML(3pm) User Contributed Perl Documentation Pod::Tree::HTML(3pm)


Pod::Tree::HTML - Generate HTML from a Pod::Tree


  use Pod::Tree::HTML;
  $source   =   Pod::Tree->new(%options);
  $source   =  "file.pod";
  $source   =   IO::File->new;
  $source   = \$pod;
  $source   = \@pod;
  $dest     =   HTML::Stream->new;
  $dest     =   IO::File->new;
  $dest     =  "file.html";
  $html     =   Pod::Tree::HTML->new($source, $dest, %options);
  @values   = $html->get_options(@keys);
  $fragment = $html->escape_2396 ($section);
  $url      = $html->assemble_url($base, $page, $fragment);


"HTML::Stream", "Text::Template"


"Pod::Tree::HTML" reads a POD and translates it to HTML. The source and destination are fixed when the object is created. Options are provided for controlling details of the translation.

The "translate" method does the actual translation.

For convenience, "Pod::Tree::HTML" can read PODs from a variety of sources, and write HTML to a variety of destinations. The "new" method resolves the $source and $dest arguments.

"Pod::Tree::HTML" can also use "Text::Template" to fill in an HTML template file.

Source resolution

"Pod::Tree::HTML" can obtain a POD from any of 5 sources. "new" resolves $source by checking these things, in order:

If $source "isa" "POD::Tree", then the POD is taken from that tree.
If $source is not a reference, then it is taken to be the name of a file containing a POD.
If $source "isa" "IO::File", then it is taken to be an "IO::File" object that is already open on a file containing a POD.
If $source is a SCALAR reference, then the text of the POD is taken from that scalar.
if $source is an ARRAY reference, then the paragraphs of the POD are taken from that array.

If $source isn't any of these things, "new" "die"s.

Destination resolution

"Pod::Tree::HTML" can write HTML to any of 5 destinations. "new" resolves $dest by checking these things, in order:

If $dest "isa" "HTML::Stream", then "Pod::Tree::HTML" writes HTML to that stream.
If $dest "isa" "IO::File", then "Pod::Tree::HTML" writes HTML to that file.
If $dest has a "print" method, then "Pod::Tree::HTML" passes HTML to that method.
If $dest is a SCALAR reference, then "Pod::Tree::HTML" writes HTML to that scalar.
If $dest is a string, then "Pod::Tree::HTML" writes HTML to the file with that name.

If $dest isn't any of these things, "new" "die"s.


$html = "new" "Pod::Tree::HTML" $source, $dest, %options
Creates a new "Pod::Tree::HTML" object.

$html reads a POD from $source, and writes HTML to $dest. See "Source resolution" and "Destination resolution" for details.

Options controlling the translation may be passed in the %options hash. See "OPTIONS" for details.

Sets options controlling the translation. See "OPTIONS" for details.
@values = $html->"get_options"(@keys)
Returns the current values of the options specified in @keys. See "OPTIONS" for details.
Translates the POD to HTML. This method should only be called once.

In the second form, $template is the name of a file containing a template. The template will be filled in by the "Text::Template" module. Here is a minimal template, showing example usage of all the variables that are set by "Pod::Tree::HTML".

    <base href="{$base}">
    <link href="{$css}" rel="stylesheet" type="text/css">
   <body bgcolor="{$bgcolor}" text="{$text}">

The program fragments in the template are evaulted in the "Pod::Tree::HTML" package. Any variables that you set in this package will be available to your template.

When a template is used, the destination must not be an "HTML::Stream" object.

"translate" doesn't return anything. The first form always returns. The second form "die"s if there is an error creating or filling in the template.

Emits the table of contents and body of the HTML document.

These methods are called automatically by "translate". They are exposed in the API for applications that wish to embed the HTML inside a larger document.

Utility methods

These methods are provided for implementors who write their own link mapper objects.

$fragment = $html->"escape_2396"($section)
Escapes $section according to RFC 2396. For example, the section

    some section

is returned as

$url = $html->"assemble_url"($base, $page, $fragment)
Assembles $base, $page, and $fragment into a URL, of the form


Attempts to construct a valid URL, even if some of $base, $page, and $fragment are empty.


"base" => $url
Specifies a base URL for relative HTML links.
"bgcolor" => #rrggbb
Set the background color to #rrggbb. Default is white.
"css" => $url
Specifies a Cascading Style Sheet for the generated HTML page.
"depth" => $depth
Specifies the depth of the generated HTML page in a directory tree. See "LINK MAPPING" for details.
"empty" => 1
Causes the "translate" method to emit an HTML file, even if the POD is empty. If this option is not provided, then no HTML file is created for empty PODs.
"hr" => $level
Controls the profusion of horizontal lines in the output, as follows:

    $level   horizontal lines
    0          none
    1          between TOC and body
    2          after each =head1
    3          after each =head1 and =head2

Default is level 1.

"link_map" => $link_map
Sets the link mapper. See "LINK MAPPING" for details.
"text" => #rrggbb
Set the text color to #rrggbb. Default is black.
"title" => title
Set the page title to title. If no "title" option is given, "Pod::Tree::HTML" will attempt construct a title from the second paragrah of the POD. This supports the following style:

    =head1 NAME
    ls - list contents of directory
"toc" => [0|1]
Includes or omits the table of contents. Default is to include the TOC.


"Pod::Tree::HTML" automatically generates HTML destination anchors for all =headn command paragraphs, and for text items in =over lists. The text of the paragraph becomes the "name" attribute of the anchor. Markups are ignored and the text is escaped according to RFC 2396.

For example, the paragraph

    =head1 C<Foo> Bar

is translated to

    <h1><a name="Foo%20Bar"><code>Foo</code> Bar</a></h1>

To link to a heading, simply give the text of the heading in an "L<>" markup. The text must match exactly; markups may vary. Either of these would link to the heading shown above

    L</C<Foo> Bar>
    L</Foo Bar>

To generate destination anchors in other places, use the index ("X<>") markup

    We can link to X<this text> this text.

and link to it as usual

    L</this text> uses the index markup.

Earlier versions of this module also emitted the content of the X<> markup as visible text. However, perlpod now specifies that X<> markups render as an empty string, so "Pod::Tree::HTML" has been changed to do that.


The POD specification provides the "L<>" markup to link from one document to another. HTML provides anchors ("<a href=""></a>") for the same purpose. Obviously, a POD2HTML translator should convert the first to the second.

In general, this is a hard problem. In particular, the POD format is not powerful enough to support the kind of hyper-linking that people want in a complex documentation system.

Rather than try to be all things to all people, "Pod::Tree::HTML" uses a link mapper object to translate the target of a POD link to a URL. The default link mapper does a simple translation, described below. If you don't like the default translation, you can provide your own link mapper with the ""link_map" => $link_map" option.


The default link mapper obtains the page and section from the target. It translates "::" sequences in the page to "/", and returns a URL of the form ["../"...][page".html"]["#"section]

If the ""depth" => $depth" option is given, a corresponding number of "../" sequences are prepended to page.

This is a relative URL, so it will be interpreted relative to the ""base" => $url" option, if any.


To use your own link mapper, create a link mapper object and provide it to "Pod::Tree::HTML" with the "link_map" option

    sub MyMapper::new { bless {}, shift }
    sub MyMapper::url
        my($mapper, $html, $target) = @_;
    return $url;
    $mapper = MyMapper->new;
    $html   = Pod::Tree::HTML->new(link_map => $mapper);

Your object should implement one method

$url = $mapper->"url"($html, $target)
When $html->"translate"() encounters an "L<>" markup, it calls $mapper->"url". $html is the "Pod::Tree::HTML" object itself. $target is a "Pod::Tree::Node" object representing the the target of the link. See "target nodes" in Pod::Tree::Node for information on interpreting $target.

The "url" method must return a string, which will be emitted as the value of the "href" attribute of an HTML anchor: "<a href=""$url"">"..."</a>"

"Pod:Tree:HTML" provides the "escape_2396" and "assemble_url" methods for convenience in implementing link mappers.

If the link mapper does not provide a "url" method, "Pod::Tree::HTML" will call "map"

($base, $page, $section) = $mapper->"map"($base, $page, $section, $depth);
is the URL given in the "base" option.
is the man page named in the L<> markup.
is the man page section given in the L<> markup.
is the value of the "depth" option.

The "map" method may perform arbitrary mappings on its arguments. "Pod::Tree::HTML" takes the returned values and constructs a URL of the form [$base/][$page".html"]["#"$fragment]

The "map" method is

  • deprecated
  • less flexible than the "url" method
  • supported for backwards compatibility with older versions of "Pod::Tree::HTML"


"Pod::Tree::HTML::new: not enough arguments"
(F) "new" called with fewer than 2 arguments.
"Pod::Tree::HTML::new: Can't load POD from $source"
(F) "new" couldn't resolve the $source argument. See "Source resolution" for details.
"Pod::Tree::HTML::new: Can't write HTML to $dest"
(F) "new" couldn't resolve the $dest argument. See "Destination resolution" for details.
"Pod::Tree::HTML::new: Can't open $dest: $!"
(F) The destination file couldn't be opened.


perl(1), "Pod::Tree", "Pod::Tree::Node", "Text::Template"


Steven McDougall,


Copyright (c) 1999-2009 by Steven McDougall. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

2019-02-25 perl v5.28.1