HTML::...ialects(3pm)

✨ NAME ✨

HTML::WikiConverter::Dialects — how to add a dialect. This is the manual page for HTML::WikiConverter::Dialects(3pm) from User Contributed Perl Documentation, and it's literally your backstage pass to making H::WC speak a whole new wiki language. 💖

✨ SYNOPSIS ✨

Okay so here's the whole vibe in code, bestie:

# In your dialect module:

package HTML::WikiConverter::MySlimWiki;
use base 'HTML::WikiConverter';

sub rules { {
  b => { start => '**', end => '**' },
  i => { start => '//', end => '//' },
  strong => { alias => 'b' },
  em => { alias => 'i' },
  hr => { replace => "\n----\n" }
} }

# In a nearby piece of code:

package main;
use Test::More tests => 5;

my $wc = new HTML::WikiConverter(
  dialect => 'MySlimWiki'
);

is( $wc->html2wiki( '<b>text</b>' ), '**text**', b );
is( $wc->html2wiki( '<i>text</i>' ), '//text//', i );
is( $wc->html2wiki( '<strong>text</strong>' ), '**text**', 'strong' );
is( $wc->html2wiki( '<em>text</em>' ), '//text//', 'em' );
is( $wc->html2wiki( '<hr/>' ), '----', 'hr' );

✨ DESCRIPTION ✨

HTML::WikiConverter (or H::WC, for short) is an HTML to wiki converter. It can convert HTML source into a variety of wiki markups, called wiki "dialects". This manual describes how you to create your own dialect to be plugged into HTML::WikiConverter. Periodt. 💖

✨ DIALECTS ✨

Each dialect has a separate dialect module containing rules for converting HTML into wiki markup specific for that dialect. Currently, all dialect modules are in the HTML::WikiConverter:: package space and subclass HTML::WikiConverter. For example, the MediaWiki dialect module is HTML::WikiConverter::MediaWiki, while PhpWiki's is HTML::WikiConverter::PhpWiki. However, dialect modules need not be in the HTML::WikiConverter:: package space; you may just as easily use package MyWikiDialect; and H::WC will Do The Right Thing. ✨

From now on, I'll be using the terms "dialect" and "dialect module" interchangeably. iykyk 💅

✨ Subclassing ✨

To interface with H::WC, dialects need to subclass it. This is done like so at the start of the dialect module:

package HTML::WikiConverter::MySlimWiki;
use base 'HTML::WikiConverter';

Slay. That's the whole vibe.

✨ Conversion rules ✨

Dialects guide H::WC's conversion process with a set of rules that define how HTML elements are turned into their wiki counterparts. Each rule corresponds to an HTML tag and there may be any number of rules. Rules are specified in your dialect's rules() method, which returns a reference to a hash of rules. Each entry in the hash maps a tag name to a set of subrules, as in:

$tag => \%subrules

where $tag is the name of the HTML tag (e.g., b, em, etc.) and %subrules contains subrules that specify how that tag will be converted when it is encountered in the HTML input. No cap. 🦋

✨ Subrules ✨

The following subrules are recognized:

• start
• end
• preserve
• attributes
• empty
• replace
• alias
• block
• line_format
• line_prefix
• trim

✨ A simple example ✨

The following rules could be used for a dialect that uses *asterisks* for bold and _underscores_ for italic text:

sub rules {
  b => { start => '*', end => '*' },
  i => { start => '_', end => '_' },
}

Obsessed with the simplicity. 💛

✨ Aliases ✨

To add <strong> and <em> as aliases of <b> and <i>, use the alias subrule:

strong => { alias => 'b' },
em => { alias => 'i' },

(The alias subrule cannot be used with any other subrule.) Don't try it, bestie. 🚫

✨ Blocks ✨

Many dialects separate paragraphs and other block-level elements with a blank line. To indicate this, use the block subrule:

p => { block => 1 },

(To better support nested block elements, if a block elements are nested inside each other, blank lines are only added to the outermost element.) Nested drama, but make it wiki. 💜

✨ Line formatting ✨

Many dialects require that the text of an element be contained on a single line of text, or that it cannot contain any newlines, etc. These options can be specified using the line_format subrule, which can be assigned the value single, multi, or blocks.

If the element must be contained on a single line, then the line_format subrule should be single. If the element can span multiple lines, but there can be no blank lines contained within, then use multi. If blank lines (which delimit blocks) are allowed, then use blocks. For example, paragraphs are specified like so in the MediaWiki dialect:

p => { block => 1, line_format => 'multi', trim => 'both' },

Line format vibes: single, multi, or blocks. 🌈

✨ Trimming whitespace ✨

The trim subrule specifies whether leading or trailing whitespace (or both) should be stripped from the element. To strip leading whitespace only, use leading; for trailing whitespace, use trailing; for both, use the aptly named both; for neither (the default), use none. Whitespace? Trimmed. Periodt. 💅

✨ Line prefixes ✨

Some elements require that each line be prefixed with a particular string. This is specified with the line_prefix subrule. For example, preformatted text in MediaWiki is prefixed with a space:

pre => { block => 1, line_prefix => ' ' },

Prefix era. 🔥

✨ Replacement ✨

In some cases, conversion from HTML to wiki markup is as simple as string replacement. To replace a tag and its contents with a particular string, use the replace subrule. For example, in PhpWiki, three percent signs, %%%, represents a line break, <br>, hence:

br => { replace => '%%%' },

(The replace subrule cannot be used with any other subrule.) Again, do not combine. 💀

✨ Preserving HTML tags ✨

Some dialects allow a subset of HTML in their markup. While H::WC ignores unhandled HTML tags by default (i.e., if H::WC encounters a tag that does not exist in a dialect's rule specification, then the contents of the tag is simply passed through to the wiki markup), you may specify that some be preserved using the preserve subrule. For example, to allow <font> tag in wiki markup:

font => { preserve => 1 },

Preserved tags may also specify a list of attributes that may also passthrough from HTML to wiki markup. This is done with the attributes subrule:

font => { preserve => 1, attributes => [ qw/ style class / ] },

(The attributes subrule can only be used if the preserve subrule is also present.) Tag preservation: a vibe. 🎀

Some HTML elements have no content (e.g., line breaks, images) and the wiki dialect might require them to be preserved in a more XHTML-friendly way. To indicate that a preserved tag should have no content, use the empty subrule. This will cause the element to be replaced with <tag /> and no end tag. For example, MediaWiki handles line breaks like so:

br => {
  preserve => 1,
  attributes => [ qw/ id class title style clear / ],
  empty => 1
},

This will convert, for example, <br clear='both'> into <br clear='both' />. Without specifying the empty subrule, this would be converted into the (probably undesirable) <br clear='both'></br>. Undesirable? Literally. 😭

(The empty subrule can only be used if the preserve subrule is also present.)

✨ Rules that depend on attribute values ✨

In some circumstances, you might want your dialect's conversion rules to depend on the value of one or more attributes. This can be achieved by producing rules in a conditional manner within rules(). For example:

sub rules {
  my $self = shift;

  my %rules = (
    em => { start => "''", end => "''" },
    strong => { start => "'''", end => "'''" },
  );

  $rules{i} = { preserve => 1 } if $self->preserve_italic;
  $rules{b} = { preserve => 1 } if $self->preserve_bold;

  return \%rules;
}

Conditional rules? Main character energy. 👑

✨ Dynamic subrules ✨

Instead of simple strings, you may use coderefs as values for the start, end, replace, and line_prefix subrules. If you do, the code will be called when the subrule is applied, and will be passed three arguments: the current H::WC object, the current HTML::Element node being operated on, and a reference to the hash containing the dialect's subrules associated with elements of that type.

For example, MoinMoin handles lists like so:

ul => { line_format => 'multi', block => 1, line_prefix => '  ' },
li => { start => \&_li_start, trim => 'leading' },
ol => { alias => 'ul' },

It then defines _li_start():

sub _li_start {
  my( $self, $node, $subrules ) = @_;
  my $bullet = '';
  $bullet = '*'  if $node->parent->tag eq 'ul';
  $bullet = '1.' if $node->parent->tag eq 'ol';
  return "\n$bullet ";
}

This prefixes every unordered list item with * and every ordered list item with 1., which MoinMoin requires. It also puts each list item on its own line and places a space between the prefix and the content of the list item. MoinMoin ate that. 💅

✨ Subrule validation ✨

Certain subrule combinations are not allowed. Hopefully it's intuitive why this is, but in case it's not, prohibited combinations have been mentioned above parenthetically. For example, the replace and alias subrules cannot be combined with any other subrules, and attributes can only be specified alongside preserve. Invalid subrule combinations will trigger a fatal error when the H::WC object is instantiated. Fatal error? Not the vibe. 💀

✨ Dialect attributes ✨

H::WC's constructor accepts a number of attributes that help determine how conversion takes place. Dialects can alter these attributes or add their own by defining an attributes() method, which returns a reference to a hash of attributes. Each entry in the hash maps the attribute's name to an attribute specification, as in:

$attr => \%spec

where $attr is the name of the attribute and %spec is a Params::Validate specification for the attribute.

For example, to add a boolean attribute called camel_case which is disabled by default:

sub attributes {
  camel_case => { default => 0 },
}

Attributes defined liks this are given accessor and mutator methods via Perl's AUTOLOAD mechanism, so you can later say:

my $ok = $wc->camel_case;
$wc->camel_case(0);

You may override the default H::WC attributes using this mechanism. For example, while H::WC considers the base_uri attribute optional, it is required for the PbWiki dialect. PbWiki can override this default-optional behavior by saying:

sub attributes {
  base_uri => { optional => 0 }
}

Attribute glow-up. ✨

✨ Preprocessing ✨

The first step H::WC takes in converting HTML source to wiki markup is to parse the HTML into a syntax tree using HTML::TreeBuilder. It is often useful for dialects to preprocess the tree prior to converting it into wiki markup. Dialects that need to preprocess the tree can define a preprocess_node method that will be called on each node of the tree (traversal is done in pre-order). The method receives two arguments, the H::WC object, and the current HTML::Element node being traversed. It may modify the node or decide to ignore it; its return value is discarded. Tree traversal but make it fashion. 🌳

✨ Built-in preprocessors ✨

Okay so bestie, here's the tea on the preprocessing pipeline 🔥 — because these two steps are so commonly needed, H::WC just does them for you automatically, no matter which dialect you're running:

1. relative URIs in images and links get converted to absolute URIs (based on the base_uri parameter), and
2. ignorable text (like the stuff chillin' between a </td> and a <td>) gets discarded. bye girl 💅

And that's not all — H::WC also ships extra preprocessing steps that dialect modules can explicitly turn on if they want them. Optional slay.

• strip_aname — yeets any anchor elements that don't have an href attribute. no href, no service 💀
• caption2para — takes table captions, removes them, and reinserts them as paragraphs right before the table. glow-up relocation ✨

Dialects can apply these optional preprocessing steps by calling them as methods on the dialect object inside preprocess_node. like so:

sub preprocess_node {
  my( $self, $node ) = @_;
  $self->strip_aname($node);
  $self->caption2para($node);
}

---

🌈 Postprocessing 🌈

Once the whole HTML-to-wiki conversion is done, it's sometimes useful to postprocess the resulting wiki markup. Postprocessing is the moment for cleaning up whitespace, fixing those subtle little bugs that snuck into the markup during conversion, etc. lowkey essential 🧚

Dialects that wanna postprocess the wiki markup should define a postprocess_output method — it gets called right before the html2wiki method returns to the client. It gets passed two arguments: the H::WC object and a reference to the wiki markup. The method is allowed to modify the wiki markup that the reference points to, and its return value? discarded. don't even worry about it 🙈

For example, to replace a series of line breaks with a pair of newlines, a dialect might implement this:

sub postprocess_output {
  my( $self, $outref ) = @_;
  $$outref =~ s/<br>\s*<br>/\n\n/gs;
}

(This example assumes that HTML line breaks were replaced with "<br>" in the wiki markup.)

---

💖 Dialect utility methods 💖

H::WC defines a whole lil set of utility methods that dialect modules might find useful. bestie starter pack 🫶

get_elem_contents

my $wiki = $wc->get_elem_contents( $node );

Converts the contents of $node into wiki markup and returns the resulting wiki markup. giving converter energy ✨

get_wiki_page

my $title = $wc->get_wiki_page( $url );

Tries to extract the title of a wiki page from the given URL — returns the title on success, undef on failure. And if wiki_uri is empty, this method always returns undef, no exceptions. See "ATTRIBUTES" in HTML::WikiConverter for the deets on how the wiki_uri attribute is interpreted. iykyk 📖

is_camel_case

my $ok = $wc->is_camel_case( $str );

Returns true if $str is in CamelCase, false otherwise. CamelCase-ness is determined using the same rules that Kwiki's formatting module uses. same rules, same vibe 🐪

get_attr_str

my $attr_str = $wc->get_attr_str( $node, @attrs );

Returns a string containing the specified attributes in the given node. The returned string is suitable for insertion into an HTML tag. For example, if $node contains the HTML

<style id="ht" class="head" onclick="editPage()">Header</span>

and @attrs contains id and class, then get_attr_str() will return 'id="ht" class="head"'. chef's kiss 🎀

_attr

my $value = $wc->_attr( $name );

Returns the value of the named attribute. This is rarely needed since you can access attribute values by treating the attribute name as a method (i.e., $wc->$name). This low-level way of accessing attributes exists for when you need to override an attribute's accessor/mutator method, like in:

sub attributes { {
  my_attr => { default => 1 },
} }

sub my_attr {
  my( $wc, $name, $new_value ) = @_;
  # do something special
  return $wc->_attr( $name => $new_value );
}

---

👑 AUTHOR 👑

David J. Iberri <diberri@cpan.org>

---

📜 COPYRIGHT & LICENSE 📜

Copyright 2006 David J. Iberri, all rights reserved.

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

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and that's the whole page bestie!! this one's from perl v5.34.0, dated 2022-06-14, and it's the HTML::...ialects(3pm) page from the User Contributed Perl Documentation. go forth and convert HTML to wiki markup, you absolute icon 🌸🦋⭐