- From: Steve Zilles <szilles@adobe.com>
- Date: Thu, 16 Jun 2005 10:29:55 -0700
- To: fantasai <fantasai.lists@inkedblade.net>, Erik van der Poel <erik@vanderpoel.org>
- Cc: Unicode Mailing List <unicode@unicode.org>, www-style@w3.org, www-international@w3.org
- Message-id: <6.2.1.2.2.20050616102319.040ed428@mailsj-v1.corp.adobe.com>
At 03:14 PM 6/13/2005, fantasai wrote: >Erik van der Poel wrote: >>[I'm not on the www-style list.] >>fantasai wrote: >> >>> For characters within the same inline sequence. >>> >>> 1. Shaping and joining behavior MUST NOT be affected by element >>> boundaries. >>If the CSS "display" property is set to "none" for a particular element, >>then perhaps the characters in adjacent displayable elements should not >>be joined to the characters in the "display: none" element. >>(Maybe you already thought of this, and that is what is meant by "same >>inline sequence"?) > >No, I hadn't thought of that. But if an element is display: none, then >for all rendering purposes it is to be treated as if it wasn't there. > >>> 4. Obligatory ligatures MUST NOT be broken if the formatting rules >>> introduce no extra space between the affected characters, even >>> if this means some of the characters are rendered in the wrong >>> font or as part of the wrong visual element. >>Perhaps the spec could say that an implementation MAY honor such things >>as a color change (which may not be possible in current font technologies >>such as OpenType?) > >Of course if the system is somehow capable of honoring both the style >rules and the ligature formation, it should be allowed to do so. :) > >>or MAY instead use the isolated forms of the individual characters. I >>don't know whether the obligatory ligature rules should trump the style rules. > >Yeah, I'm not too set on this one. But I don't know how critical it is >for the affected scripts. If the font isn't changing at all, though, then >the spec should require that the ligature be formed across element >boundaries. I suspect it might be simpler just to make the exception apply >even in cases where the font changes. For what it is worth the following text comes from the XSL 1.0 REC concerning when a ligature substitution is to be done. From section 4.7.2 Line Building: ...substitutions may occur because of addition of hyphens or spelling changes due to hyphenation, or glyph image construction from syllabification, or ligature formation. Substitutions that replace a sequence of glyph-areas with a single glyph-area should only occur when the margin, border, and padding in the inline-progression-direction (start- and end-), baseline-shift, and letter-spacing values are zero, treat-as-word-space is false, and the values of all other relevant traits match (i.e., alignment-adjust, alignment-baseline, color trait, background traits, dominant-baseline-identifier, font traits, text-depth, text-altitude, glyph-orientation-horizontal, glyph-orientation-vertical, line-height, lineheight-shift-adjustment, text-decoration, text-shadow). This indicates a bias to honoring the author's/user's styling choices over ligature formation. I am not sure how well these paragraphs have been tested in practice. >>> 5. Combining characters MUST be rendered as the combined grapheme >>> cluster if the system is capable of rendering the combination, >>> even if this means some of the characters are rendered in the >>> wrong font or as part of the wrong visual element. The combined >>> grapheme cluster SHOULD be rendered as part of the base >>> character's element, or, in the case of combining jamos, the >>> initial character's element. >>Here again, shouldn't the style rules trump the Unicode rules? Otherwise, >>why should we even allow tags to be inserted between such characters? > >In this case, I think it's more important for the grapheme cluster to >be rendered as one unit. An 'a' with an acute accent should have its >acute accent on top, and a Hangul syllable expressed as individual >pieces should be presented as its proper syllable block. Breaking >ligatures like alef-lam looks weird, but it wouldn't be as bad as >breaking such combinations: alef and lam appear individually quite >frequently, but combining vowels and diacritics don't. > >~fantasai Steve ===================================== Steve Zilles 115 Lansberry Court, Los Gatos, CA 95032-4710 steve@zilles.org
Received on Thursday, 16 June 2005 17:30:18 UTC