From: Richard Wordingham (richard.wordingham@ntlworld.com)
Date: Thu Apr 13 2006 - 15:55:33 CST
Karl Pentzlin wrote on Thursday, April 13, 2006 at 9:48 AM:
>I try to understand whether "E" + CGJ + "s" + CGJ + "c" + U+20E3
> COMBINING ENCLOSING KEYCAP should produce a representation of an
> "Esc" key in plain text (given an appropriate font rendering
> mechanism).
> I refer to the phrase "The combining enclosing marks apply to a
> preceding default grapheme cluster." (printed edition of "The Unicode
> <standard V4.0", p.188).
TUS 4.0 Section 15.2 p392
http://www.unicode.org/versions/Unicode4.0.0/ch15.pdf says:
"For rendering, the combining grapheme joiner is invisible. However, some
older implementationsmay treat a sequence of grapheme clusters linked by
combining grapheme joiners as a single unit for the application of enclosing
combining marks."
In other words, it may once have worked, but it shoudn't work now.
> Does the Combining Grapheme Joiner (CGJ, U+034F) constitute a grapheme
> cluster in the sense of UAX 29 "Text boundaries"?
> http://www.unicode.org/reports/tr29/
> I did not find any evidence there. (Maybe I overlooked something or
> searched in the wrong place?)
Yes - see for example
http://www.unicode.org/Public/4.1.0/ucd/auxiliary/GraphemeBreakProperty.txt
.
However, that does not help, for a CGJ is the final character in a *default*
grapheme cluster unless it is followed by another character with the
'extend' property.
> Or is producing multi-letter key representations in plain text done
> by another mechanism as CGJ (e.g. ZWJ), or is it subject to higher level
> protocols at all?
It would seem it can't be done for plain text.
Richard.
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