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Subject: [docbook-tc] bidi override thoughts
At 18:45 2002 08 20 -0400, Norman Walsh wrote: >| 573419 Add bidirectional text overrides > >Add bdo everywhere? > >ACTION: Paul to investigate what the content model needs to be and why simply > using a nested phrase is insufficient. XSL-FO discusses BIDI concepts at [1]. (By the way, the maximum nesting of direction changes is 61!) Most of the discussion in this section has to do with character-level BIDI switching, so it is less relevant to the case at hand. However, it does say: As defined in [UNICODE UAX #9], the Unicode BIDI algorithm takes a stream of text as input, and proceeds in three main phases: 1. Separation of the input text into paragraphs. The rest of the algorithm affects only the text between paragraph separators. . . . This implies that any bidi-override would only occur within paragraphs. However, it is unclear what Unicode means by "paragraphs." XSL-FO defines the fo:bidi-override formatting object [2]. Its "content model" is (#PCDATA|%inline;|%block;)* which pretty much allows everything. fo:bidi-override itself is part of %inline. I think this translates into DocBook as allowing bidi-override as part of %para.char.mix; and giving it a content model of (%para.char.mix;)*. If so, then I note that phrase is defined as part of %gen.char.class; which is part of %para.char.mix; and that the declaration for phrase is: <!ELEMENT phrase (%para.char.mix;)*> It sure sounds like this would allow us to use phrase to signal bidi-override if that's what we want to do. The phrase element currently has common attributes and a role attribute. That appears to leave us the option of just using the role attribute to trigger bidi-override or adding another attribute especially for triggering the bidi-override semantic. I don't think there is any need for further options to bidi-override, so if we add a new attribute, it would just be a "boolean" attribute. paul [1] http://www.w3.org/TR/xsl/slice5.html#section-N6720-Unicode-BIDI-Processing [UNICODE UAX #9] http://www.unicode.org/unicode/reports/tr9/ [2] http://www.w3.org/TR/xsl/slice6.html#fo_bidi-override
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