Thank you, Ken! What about Grapheme_Extend class characters placed out of context? It would be nice to see a dotted box in cases like AׁB (U+0041 U+05C1 HEBREW POINT SHIN DOT U+0042)
Leo On 3/6/12, Ken Whistler <[email protected]> wrote: >> I see. I was under an impression that the renderer must avoid >> rendering such characters visibly if at all possible. > > Ah, a teachable moment! > > There is a distinction in the Unicode Standard between default ignorable > code > points and other characters, regarding the recommendations of the standard > for fallback rendering. > > For default ignorable code points, the recommendation is, indeed, to just > display nothing when your renderer cannot otherwise handle proper rendering > of the character's intended effect. That is what you do, for example, > with a ZWJ > that is otherwise out of place or not supported for rendering in a > particular > context. (The exception would be for a Show Hidden mode, when you want > to see *everything*.) > > For other characters, *including* viramas as a class, the fallback > recommendation > is to display something visible. Don't be fooled by the fact that the > Khmer COENG > is shown in the code charts with a dotted box and has no visible display > of its > own as a separate mark -- unlike typical Indic viramas. It is still > better, in general, > to know that a virama is present (or in this case a COENG) in text, even > if you cannot > display its intended effect properly if you stick it in the wrong sequences. > > For background on this topic, see Section 5.21, Default Ignorable Code > Points, > in the standard: > > http://www.unicode.org/versions/Unicode6.0.0/ch05.pdf > > For a complete list of default ignorable code points (which do not > include U+17D2), > see: > > http://www.unicode.org/Public/UNIDATA/DerivedCoreProperties.txt > > Down towards the bottom of that data file, you will also find a list of > all the > Grapheme_Link characters, which is identical to ccc=Virama, and > constitutes the > list of all the characters that are *structural* viramas in the > standard, whether > they are specifically termed a virama in a particular script or not. > That list > *does* include U+17D2. And none of the viramas is a default ignorable code > point. > > --Ken > >
