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HTML::WikiConverter::DUsercContributed Perl DoHTML::WikiConverter::Dialects(3)

       HTML::WikiConverter::Dialects - How to add a dialect

	 # 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' );

       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.

       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"

       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';

   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.


       The following subrules are recognized:






       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 => '_' },


       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.)


       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

       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' },

       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".

       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 => ' ' },


       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.)

       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.)

       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>".

       (The "empty" subrule can	only be	used if	the "preserve" subrule is also

       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

	 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;

   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.

   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

   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;

       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 }

       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

       Built-in	preprocessors

       Because they are	commonly needed, H::WC automatically carries out two
       preprocessing steps, regardless of the dialect: 1) relative URIs	in
       images and links	are converted to absolute URIs (based upon the
       "base_uri" parameter), and 2) ignorable text (e.g. between a "</td>"
       and "<td>") is discarded.

       H::WC also provides additional preprocessing steps that may be
       explicitly enabled by dialect modules.

	   Removes any anchor elements that do not contain an "href"

	   Removes table captions and reinserts	them as	paragraphs before the

       Dialects	may apply these	optional preprocessing steps by	calling	them
       as methods on the dialect object	inside "preprocess_node". For example:

	 sub preprocess_node {
	   my( $self, $node ) =	@_;

       Once the	work of	converting HTML	is complete, it	is sometimes useful to
       postprocess the resulting wiki markup. Postprocessing can be used to
       clean up	whitespace, fix	subtle bugs introduced in the markup during
       conversion, etc.

       Dialects	that want to postprocess the wiki markup should	define a
       "postprocess_output" method that	will be	called just before the
       "html2wiki" method returns to the client. The method will be passed two
       arguments, the H::WC object and a reference to the wiki markup. The
       method may modify the wiki markup that the reference points to; its
       return value is discarded.

       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 set of utility methods that dialect modules may find


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

       Converts	the contents of	$node into wiki	markup and returns the
       resulting wiki markup.


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

       Attempts	to extract the title of	a wiki page from the given URL,
       returning the title on success, "undef" on failure. If "wiki_uri" is
       empty, this method always return	"undef". See "ATTRIBUTES" in
       HTML::WikiConverter for details on how the "wiki_uri" attribute is


	 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.


	 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"'.


	 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 method of accessing
       attributes is provided for when you need	to override an attribute's
       accessor/mutator	method,	as in:

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

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

       David J.	Iberri <>

       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.

perl v5.32.1			  2008-05-18  HTML::WikiConverter::Dialects(3)


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