- From: Myles C. Maxfield via GitHub <sysbot+gh@w3.org>
- Date: Fri, 16 Dec 2016 17:40:50 +0000
- To: public-css-archive@w3.org
For triggering emoji presentation style (often triggered by variation selectors), [UTR51](http://www.unicode.org/reports/tr51/proposed.html#Presentation_Style) explicitly states "Some systems may also provide this distinction with higher-level markup, rather than variation sequences." Therefore, the `text-transform` property should not be used to trigger this type of presentation style, since this behavior may not actually transform text. Similarly, the `font-variant` properties should also not be used because implementation of this behavior does not use font features. This behavior is implemented by the 'cmap' table in the font. That is, drawing the string U+2603 U+FE0E in a font may actually end up drawing a different glyph ID than if you drew the string U+2603 U+FE0F using the same font. This has particular implications for font fallback - the strings above may map to glyph ID 0, which means that a fallback font may be chosen. This affects layout because the fallback font may have different metrics than the requested font. On the other hand, color palettes are implemented after glyph selection, meaning they have no affect on font fallback. Palette selection describes how to draw a glyph once you already have a glyph ID in hand. Importantly, it also can't change the metrics of the glyph, meaning it doesn't affect layout. Because of this, the two concepts should be kept separate, and should be triggered with orthogonal properties. Telling a font to draw with a text presentation while also specifying a color palette should be legal and valid. (Perhaps most fonts won't react to the color palette in this situation, but it's totally possible to build a font which would.) -- GitHub Notification of comment by litherum Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/352#issuecomment-267651758 using your GitHub account
Received on Friday, 16 December 2016 17:40:56 UTC