1HTML::WikiConverter::DiUasleerctCso(n3t)ributed Perl DocHuTmMeLn:t:aWtiikoinConverter::Dialects(3)
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6 HTML::WikiConverter::Dialects - How to add a dialect
7
9 # In your dialect module:
10 package HTML::WikiConverter::MySlimWiki;
12 use base 'HTML::WikiConverter';
13 sub rules { {
15 b => { start => '**', end => '**' },
16 i => { start => '//', end => '//' },
17 strong => { alias => 'b' },
18 em => { alias => 'i' },
19 hr => { replace => "\n----\n" }
20 } }
21 # In a nearby piece of code:
23 package main;
25 use Test::More tests => 5;
26 my $wc = new HTML::WikiConverter(
28 dialect => 'MySlimWiki'
29 );
30 is( $wc->html2wiki( '<b>text</b>' ), '**text**', b );
32 is( $wc->html2wiki( '<i>text</i>' ), '//text//', i );
33 is( $wc->html2wiki( '<strong>text</strong>' ), '**text**', 'strong' );
34 is( $wc->html2wiki( '<em>text</em>' ), '//text//', 'em' );
35 is( $wc->html2wiki( '<hr/>' ), '----', 'hr' );
36
38 HTML::WikiConverter (or H::WC, for short) is an HTML to wiki converter.
39 It can convert HTML source into a variety of wiki markups, called wiki
40 "dialects". This manual describes how you to create your own dialect
41 to be plugged into HTML::WikiConverter.
42
44 Each dialect has a separate dialect module containing rules for
45 converting HTML into wiki markup specific for that dialect. Currently,
46 all dialect modules are in the "HTML::WikiConverter::" package space
47 and subclass HTML::WikiConverter. For example, the MediaWiki dialect
48 module is HTML::WikiConverter::MediaWiki, while PhpWiki's is
49 HTML::WikiConverter::PhpWiki. However, dialect modules need not be in
50 the "HTML::WikiConverter::" package space; you may just as easily use
51 "package MyWikiDialect;" and H::WC will Do The Right Thing.
52 From now on, I'll be using the terms "dialect" and "dialect module"
54 interchangeably.
55 Subclassing
57 To interface with H::WC, dialects need to subclass it. This is done
58 like so at the start of the dialect module:
59 package HTML::WikiConverter::MySlimWiki;
61 use base 'HTML::WikiConverter';
62 Conversion rules
64 Dialects guide H::WC's conversion process with a set of rules that
65 define how HTML elements are turned into their wiki counterparts. Each
66 rule corresponds to an HTML tag and there may be any number of rules.
67 Rules are specified in your dialect's rules() method, which returns a
68 reference to a hash of rules. Each entry in the hash maps a tag name to
69 a set of subrules, as in:
70 $tag => \%subrules
72 where $tag is the name of the HTML tag (e.g., "b", "em", etc.) and
74 %subrules contains subrules that specify how that tag will be converted
75 when it is encountered in the HTML input.
76 Subrules
78 The following subrules are recognized:
80 start
82 end
83 preserve
85 attributes
86 empty
87 replace
89 alias
90 block
92 line_format
93 line_prefix
94 trim
96 A simple example
98 The following rules could be used for a dialect that uses "*asterisks*"
100 for bold and "_underscores_" for italic text:
101 sub rules {
103 b => { start => '*', end => '*' },
104 i => { start => '_', end => '_' },
105 }
106 Aliases
108 To add "<strong>" and "<em>" as aliases of "<b>" and "<i>", use the
110 "alias" subrule:
111 strong => { alias => 'b' },
113 em => { alias => 'i' },
114 (The "alias" subrule cannot be used with any other subrule.)
116 Blocks
118 Many dialects separate paragraphs and other block-level elements with a
120 blank line. To indicate this, use the "block" subrule:
121 p => { block => 1 },
123 (To better support nested block elements, if a block elements are
125 nested inside each other, blank lines are only added to the outermost
126 element.)
127 Line formatting
129 Many dialects require that the text of an element be contained on a
131 single line of text, or that it cannot contain any newlines, etc. These
132 options can be specified using the "line_format" subrule, which can be
133 assigned the value "single", "multi", or "blocks".
134 If the element must be contained on a single line, then the
136 "line_format" subrule should be "single". If the element can span
137 multiple lines, but there can be no blank lines contained within, then
138 use "multi". If blank lines (which delimit blocks) are allowed, then
139 use "blocks". For example, paragraphs are specified like so in the
140 MediaWiki dialect:
141 p => { block => 1, line_format => 'multi', trim => 'both' },
143 Trimming whitespace
145 The "trim" subrule specifies whether leading or trailing whitespace (or
147 both) should be stripped from the element. To strip leading whitespace
148 only, use "leading"; for trailing whitespace, use "trailing"; for both,
149 use the aptly named "both"; for neither (the default), use "none".
150 Line prefixes
152 Some elements require that each line be prefixed with a particular
154 string. This is specified with the "line_prefix" subrule. For example,
155 preformatted text in MediaWiki is prefixed with a space:
156 pre => { block => 1, line_prefix => ' ' },
158 Replacement
160 In some cases, conversion from HTML to wiki markup is as simple as
162 string replacement. To replace a tag and its contents with a particular
163 string, use the "replace" subrule. For example, in PhpWiki, three
164 percent signs, "%%%", represents a line break, "<br>", hence:
165 br => { replace => '%%%' },
167 (The "replace" subrule cannot be used with any other subrule.)
169 Preserving HTML tags
171 Some dialects allow a subset of HTML in their markup. While H::WC
173 ignores unhandled HTML tags by default (i.e., if H::WC encounters a tag
174 that does not exist in a dialect's rule specification, then the
175 contents of the tag is simply passed through to the wiki markup), you
176 may specify that some be preserved using the "preserve" subrule. For
177 example, to allow "<font>" tag in wiki markup:
178 font => { preserve => 1 },
180 Preserved tags may also specify a list of attributes that may also
182 passthrough from HTML to wiki markup. This is done with the
183 "attributes" subrule:
184 font => { preserve => 1, attributes => [ qw/ style class / ] },
186 (The "attributes" subrule can only be used if the "preserve" subrule is
188 also present.)
189 Some HTML elements have no content (e.g., line breaks, images) and the
191 wiki dialect might require them to be preserved in a more XHTML-
192 friendly way. To indicate that a preserved tag should have no content,
193 use the "empty" subrule. This will cause the element to be replaced
194 with "<tag />" and no end tag. For example, MediaWiki handles line
195 breaks like so:
196 br => {
198 preserve => 1,
199 attributes => [ qw/ id class title style clear / ],
200 empty => 1
201 },
202 This will convert, for example, "<br clear='both'>" into "<br
204 clear='both' />". Without specifying the "empty" subrule, this would be
205 converted into the (probably undesirable) "<br clear='both'></br>".
206 (The "empty" subrule can only be used if the "preserve" subrule is also
208 present.)
209 Rules that depend on attribute values
211 In some circumstances, you might want your dialect's conversion rules
213 to depend on the value of one or more attributes. This can be achieved
214 by producing rules in a conditional manner within rules(). For example:
215 sub rules {
217 my $self = shift;
218 my %rules = (
220 em => { start => "''", end => "''" },
221 strong => { start => "'''", end => "'''" },
222 );
223 $rules{i} = { preserve => 1 } if $self->preserve_italic;
225 $rules{b} = { preserve => 1 } if $self->preserve_bold;
226 return \%rules;
228 }
229 Dynamic subrules
231 Instead of simple strings, you may use coderefs as values for the
232 "start", "end", "replace", and "line_prefix" subrules. If you do, the
233 code will be called when the subrule is applied, and will be passed
234 three arguments: the current H::WC object, the current HTML::Element
235 node being operated on, and a reference to the hash containing the
236 dialect's subrules associated with elements of that type.
237 For example, MoinMoin handles lists like so:
239 ul => { line_format => 'multi', block => 1, line_prefix => ' ' },
241 li => { start => \&_li_start, trim => 'leading' },
242 ol => { alias => 'ul' },
243 It then defines _li_start():
245 sub _li_start {
247 my( $self, $node, $subrules ) = @_;
248 my $bullet = '';
249 $bullet = '*' if $node->parent->tag eq 'ul';
250 $bullet = '1.' if $node->parent->tag eq 'ol';
251 return "\n$bullet ";
252 }
253 This prefixes every unordered list item with "*" and every ordered list
255 item with "1.", which MoinMoin requires. It also puts each list item on
256 its own line and places a space between the prefix and the content of
257 the list item.
258 Subrule validation
260 Certain subrule combinations are not allowed. Hopefully it's intuitive
261 why this is, but in case it's not, prohibited combinations have been
262 mentioned above parenthetically. For example, the "replace" and "alias"
263 subrules cannot be combined with any other subrules, and "attributes"
264 can only be specified alongside "preserve". Invalid subrule
265 combinations will trigger a fatal error when the H::WC object is
266 instantiated.
267 Dialect attributes
269 H::WC's constructor accepts a number of attributes that help determine
270 how conversion takes place. Dialects can alter these attributes or add
271 their own by defining an attributes() method, which returns a reference
272 to a hash of attributes. Each entry in the hash maps the attribute's
273 name to an attribute specification, as in:
274 $attr => \%spec
276 where $attr is the name of the attribute and %spec is a
278 Params::Validate specification for the attribute.
279 For example, to add a boolean attribute called "camel_case" which is
281 disabled by default:
282 sub attributes {
284 camel_case => { default => 0 },
285 }
286 Attributes defined liks this are given accessor and mutator methods via
288 Perl's "AUTOLOAD" mechanism, so you can later say:
289 my $ok = $wc->camel_case;
291 $wc->camel_case(0);
292 You may override the default H::WC attributes using this mechanism. For
294 example, while H::WC considers the "base_uri" attribute optional, it is
295 required for the PbWiki dialect. PbWiki can override this default-
296 optional behavior by saying:
297 sub attributes {
299 base_uri => { optional => 0 }
300 }
301 Preprocessing
303 The first step H::WC takes in converting HTML source to wiki markup is
304 to parse the HTML into a syntax tree using HTML::TreeBuilder. It is
305 often useful for dialects to preprocess the tree prior to converting it
306 into wiki markup. Dialects that need to preprocess the tree can define
307 a "preprocess_node" method that will be called on each node of the tree
308 (traversal is done in pre-order). The method receives two arguments,
309 the H::WC object, and the current HTML::Element node being traversed.
310 It may modify the node or decide to ignore it; its return value is
311 discarded.
312 Built-in preprocessors
314 Because they are commonly needed, H::WC automatically carries out two
316 preprocessing steps, regardless of the dialect: 1) relative URIs in
317 images and links are converted to absolute URIs (based upon the
318 "base_uri" parameter), and 2) ignorable text (e.g. between a "</td>"
319 and "<td>") is discarded.
320 H::WC also provides additional preprocessing steps that may be
322 explicitly enabled by dialect modules.
323 strip_aname
325 Removes any anchor elements that do not contain an "href"
326 attribute.
327 caption2para
329 Removes table captions and reinserts them as paragraphs before the
330 table.
331 Dialects may apply these optional preprocessing steps by calling them
333 as methods on the dialect object inside "preprocess_node". For example:
334 sub preprocess_node {
336 my( $self, $node ) = @_;
337 $self->strip_aname($node);
338 $self->caption2para($node);
339 }
340 Postprocessing
342 Once the work of converting HTML is complete, it is sometimes useful to
343 postprocess the resulting wiki markup. Postprocessing can be used to
344 clean up whitespace, fix subtle bugs introduced in the markup during
345 conversion, etc.
346 Dialects that want to postprocess the wiki markup should define a
348 "postprocess_output" method that will be called just before the
349 "html2wiki" method returns to the client. The method will be passed two
350 arguments, the H::WC object and a reference to the wiki markup. The
351 method may modify the wiki markup that the reference points to; its
352 return value is discarded.
353 For example, to replace a series of line breaks with a pair of
355 newlines, a dialect might implement this:
356 sub postprocess_output {
358 my( $self, $outref ) = @_;
359 $$outref =~ s/<br>\s*<br>/\n\n/gs;
360 }
361 (This example assumes that HTML line breaks were replaced with "<br>"
363 in the wiki markup.)
364 Dialect utility methods
366 H::WC defines a set of utility methods that dialect modules may find
367 useful.
368 get_elem_contents
370 my $wiki = $wc->get_elem_contents( $node );
372 Converts the contents of $node into wiki markup and returns the
374 resulting wiki markup.
375 get_wiki_page
377 my $title = $wc->get_wiki_page( $url );
379 Attempts to extract the title of a wiki page from the given URL,
381 returning the title on success, "undef" on failure. If "wiki_uri" is
382 empty, this method always return "undef". See "ATTRIBUTES" in
383 HTML::WikiConverter for details on how the "wiki_uri" attribute is
384 interpreted.
385 is_camel_case
387 my $ok = $wc->is_camel_case( $str );
389 Returns true if $str is in CamelCase, false otherwise. CamelCase-ness
391 is determined using the same rules that Kwiki's formatting module uses.
392 get_attr_str
394 my $attr_str = $wc->get_attr_str( $node, @attrs );
396 Returns a string containing the specified attributes in the given node.
398 The returned string is suitable for insertion into an HTML tag. For
399 example, if $node contains the HTML
400 <style id="ht" class="head" onclick="editPage()">Header</span>
402 and @attrs contains "id" and "class", then get_attr_str() will return
404 'id="ht" class="head"'.
405 _attr
407 my $value = $wc->_attr( $name );
409 Returns the value of the named attribute. This is rarely needed since
411 you can access attribute values by treating the attribute name as a
412 method (i.e., "$wc->$name"). This low-level method of accessing
413 attributes is provided for when you need to override an attribute's
414 accessor/mutator method, as in:
415 sub attributes { {
417 my_attr => { default => 1 },
418 } }
419 sub my_attr {
421 my( $wc, $name, $new_value ) = @_;
422 # do something special
423 return $wc->_attr( $name => $new_value );
424 }
425
427 David J. Iberri <diberri@cpan.org>
428
430 Copyright 2006 David J. Iberri, all rights reserved.
431 This program is free software; you can redistribute it and/or modify it
433 under the same terms as Perl itself.
434perl v5.38.0 2023-07-20 HTML::WikiConverter::Dialects(3)