[iip] Consonant clusters with a visible virama are selected as a single unit (#115)

r12a has just created a new issue for https://github.com/w3c/iip:

== Consonant clusters with a visible virama are selected as a single unit ==
<i class="meta">This issue is applicable to most languages that form conjuncts from consonant clusters using a visible virama.</i>

When the start of a line contains a 2-consonant cluster that uses a visible virama, ::first-letter should highlight only the first consonant+virama.  This corresponds to a grapheme cluster, as defined by Unicode.


<b class="subhead">Specs:</b>
[css-text-3](https://drafts.csswg.org/css-text-3/#typographic-character-unit) CSS uses the concept of <a href="https://drafts.csswg.org/css-text-3/#typographic-character-unit">'typographic character unit'</a>, which defaults to a grapheme cluster. The spec doesn't provide details about the support needed for each language.

The Unicode Consortium defines grapheme clusters to, by default, stop after the first virama in a cluster.



<b class="subhead">Tests & results:</b>
<i>Interactive test</i>, [When ::first-letter is applied to Devanagari the browser will NOT select a 2-consonant cluster as a unit if the virama is visible](https://github.com/w3c/line_paragraph_tests/issues/68)<br>
<span class="pass">Gecko</span> only highlights the initial character+virama. <span class="fail">Blink</span>, and <span class="fail">Webkit</span> select all clusters as a single unit, whether or not they are conjuncts or are rendered with a visible virama.


<b class="subhead">Priority:</b>
<i class="meta">This choice needs to be discussed.</i>  If a cluster is rendered as a conjunct, it should be selected as a single unit. If, instead, the virama is displayed (ie. it is not a conjunct) then only the initial part of the cluster should be selected. Since the underlying code points are identical if a cluster is displayed as a conjunct or instead with visible viramas, it's not possible to distinguish one situation from another by working with the code points.  In the absence of a technical solution that examines what the font used does when rendering, this is a difficult problem to solve. This priority rating says that, in the absence of a perfect solution, it is better to select a whole non-conjunct cluster than to break a conjunct.  So it is labelled advanced, rather than basic.

Please view or discuss this issue at https://github.com/w3c/iip/issues/115 using your GitHub account


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Received on Tuesday, 30 March 2021 11:21:05 UTC