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[css2] Bidi fixes based on Martin comments in msg 0274
--HG-- extra : convert_revision : svn%3A73dc7c4b-06e6-40f3-b4f7-9ed1dbc14bfc/trunk%401077
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‎css2/visuren.src‎

Lines changed: 51 additions & 36 deletions
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<html lang="en">
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<!-- $Id: visuren.src,v 2.19 1998-02-21 04:36:09 ijacobs Exp $ -->
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<!-- $Id: visuren.src,v 2.20 1998-02-23 21:25:00 ijacobs Exp $ -->
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<HEAD>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<TITLE>Visual rendering model</TITLE>
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language</a>, these properties should in most cases be used only by
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designers of document type descriptions (DTDs), or authors of special
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documents. A typical exception would be to override bidi behavior in
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a user agent if that user agent translates Yiddish to Latin
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letters at the user's request.
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a user agent if that user agent transliterates Yiddish (usually
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written with Hebrew letters) to Latin letters at the user's request.
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<P>If a document contains right-to-left characters, and if the user
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agent displays these characters (with appropriate glyphs, not
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<p>The following example shows an XML document with bidirectional
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text.</p>
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text. It illustrates an important design principle: <span
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class="index-inst" title="DTD">DTD</span> designers should take bidi
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into account both in the language proper (elements and attributes) and
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in any accompanying style sheets. The style sheets should be designed
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so that bidi rules are separate from other style rules. The bidi rules
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should not be overridden by other style sheets so that the language's
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bidi behavior is preserved.
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<div class="example"><P>
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In this example,
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</pre>
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<p>Since this is XML, the style sheet is responsible for setting the
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writing direction. (Another possibility is to use the Unicode
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characters LRE, RTF, PDF, in the text.) This is the style sheet:</p>
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writing direction. This is the style sheet:</p>
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<pre class="example">
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HEBREW {display: block; direction: rtl}
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ENGLISH {display: block; direction: ltr}
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PAR {display: block}
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EMPH {font-weight: bold}
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HE-QUO {direction: rtl; unicode-bidi: embed}
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/* Rules for bidi */
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HEBREW, HE-QUO {direction: rtl; unicode-bidi: embed}
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ENGLISH {direction: ltr; unicode-bidi: embed}
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/* Rules for presentation */
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HEBREW, ENGLISH, PAR {display: block}
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EMPH {font-weight: bold}
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</pre>
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<p>The HEBREW element is a block with a right-to-left base direction,
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<p>Because HEBREW18 must be read before english19, it is on the line
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above english19. Just breaking the long line from the earlier
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rendering would not have worked. Note also that the first syllable
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from english19 might have fit on the previous line, but one cannot
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hyphenate left-to-right words in a left-to-right context, and vice
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versa.
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from english19 might have fit on the previous line, but hyphenation of
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left-to-right words in a right-to-left context, and vice versa, is
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usually suppressed to avoid having to display a hyphen in the middle
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of a line.
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<P>Note that the default style sheet "states" that the HEWBREW, HE-QUO,
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and ENGLISH elements all create embeddings. This bidi behavior
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should be preserved even if a user decides to change 'display: inline'
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for these elements. The rules that specify 'unicode-bidi: embed'
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achieve this as long as they are not overridden by user rules.
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<!-- Should we "enforce" this with !important in the example? -IJ -->
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</div><!-- example -->
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determines the direction of several types of flow:</p>
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<ol>
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<li>When set for an <a href="#inline">inline</a>
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element or <a href="#block-level">block-level</a> element,
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it specifies the base writing direction of inline
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text generated by the element.
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<li>When set for an <a href="#inline">inline</a>
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element, it specifies the direction that generated inline
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boxes will flow into line boxes.
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<li>When set for a <a href="#block-level">block-level</a>
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element, it specifies the direction that descendant
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inline and anonymous boxes will flow into line boxes.
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<li>When set for a <a href="tables.html">table</a>
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element, it specifies the direction of table layout.
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<li>It specifies the direction that a <a
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href="visudet.html#containing-block">containing block</a> will grow
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in certain cases of content
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<li>When set for a block-level element, it specifies the base writing
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direction of inline text generated by the element. It also
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determines the position of an incomplete last line in a block
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in case of 'text-align: justify'.
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<li> When set for an inline element, in coordination with a value of
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'embed' or 'bidi-override' for the <span
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class="propinst-unicode-bidi">'unicode-bidi'</span> property, it
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specifies an additional embedding level.
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<li> When set for a table element, it specifies the direction of table
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layout.
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<li> It specifies the direction that a containing block will grow in
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certain cases of content (i.e. overflow).
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</ol>
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<P>In order to ensure the proper application of the bidirectional
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algorithm, all inline boxes within the same containing block must flow
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in the same direction (be that left-to-right or right-to-left). Even
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if a block of text contains text in both directions, inline boxes flow
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in the direction specified for the containing block. In an inline
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formatting context, non-textual entities such as images are treated as
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neutral characters, unless they are included by an element whose <span
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algorithm, inline boxes (including anonymous inline boxes) must be
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constructed, split up if necessary, and flowed so that the final order
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of the characters on each line conforms to the Unicode bidirectional
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algorithm. This means that left-to-right flow and right-to-left flow
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can occur within the same element. Non-textual entities such as images
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are treated as neutral characters, unless their <span
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class="propinst-unicode-bidi">'unicode-bidi'</span> property has a
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value other than 'normal', in which case they are treated as strong
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characters in the <span class="propinst-direction">'direction'</span>
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specified for the element.
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<div class="bidi-example"><P>
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For instance, suppose that in the middle
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of a paragraph of Hebrew (right-to-left) text, we

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