2015-02-21 08:16:38 +01:00
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Handling Content Model Changes
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1. Context
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The distinction between Transitional and Strict document types is somewhat
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of an anomaly in the lineage of XHTML document types (following 1.0, no
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doctypes do not have flavors: instead, modularization is used to let
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document authors vary their elements). This transition is usually quite
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straight-forward, as W3C usually deprecates attributes or elements, which
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are quite easily handled using tag and attribute transforms.
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However, for two elements, <blockquote>, <body> and <address>, W3C elected
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to also change the content model. <blockquote> and <body> originally
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accepted both inline and block elements, but in the strict doctype they
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only allow block elements. With <address>, the situation is inverted:
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<p> tags were now forbidden from appearing within this tag.
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2. Current situation
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Currently, HTML Purifier treats <blockquote> specially during Tidy mode
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using a custom ChildDef class StrictBlockquote. StrictBlockquote
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operates similarly to Required, except that when it encounters an inline
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element, it will wrap it in a block tag (as specified by
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%HTML.BlockWrapper, the default is <p>). The naming suggests it can
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only be used for <blockquote>s, although it may be possible to
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genericize it to work on other cases of this nature (this would be of
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little practical application, as no other element in XHTML 1.1 or earlier
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has a block-only content model).
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Tidy currently contains no custom, lenient implementation for <address>.
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If one were to be written, it would likely operate on the principle that,
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when a <p> tag were to be encountered, it would be replaced with a
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leading and trailing <br /> tag (the contents of <p>, being inline, are
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not an issue). There is no prior work with this sort of operation.
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3. Outside applicability
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There are a number of other elements that contain restrictive content
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models, such as <ul> or <span> (the latter is restrictive in that it
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does not allow block elements). In the former case, an errant node
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is eliminated completely, in the latter case, the text of the node
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would is preserved (as the parent node does allow PCDATA). Custom
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content model implementations probably are not the best way of handling
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these cases, instead, node bubbling should be implemented instead.
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vim: et sw=4 sts=4
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