Question

This string:

[NSString stringWithFormat:@"%C%C%C%C", 0x31, 0x34f, 0x32, 0x20dd]

ought to display as 12 with a circle around both characters. 0x34f is the Combining Grapheme Joiner, and 0x20dd is a combining circle.

What gets displayed is 12 with the circle around only the 2. The joiner seems to be ignored. Is there any way to get the combining grapheme joiner to work?

Answer 1

This use of Combining Grapheme Joiner is not recommended:

From the Unicode standard, Chapter 16.2 Layout Controls – Combining Grapheme Joiner

Rendering. For rendering, the combining grapheme joiner is invisible.
However, some older implementations may treat a sequence of grapheme
clusters linked by combining grapheme joiners as a single unit for the
application of enclosing combining marks. For more information on
grapheme clusters, see Unicode Technical Report #29, “Unicode Text
Segmentation.” For more information on enclosing combining marks, see
Section 3.11, Normalization Forms.

From Chapter 3.6 Combination

It should be noted, however, that older implementations may have
supported the application of an enclosing combining mark to an entire
Indic consonant conjunct or to a sequence of grapheme clusters linked
together by combining grapheme joiners. Such an approach has a number
of technical problems and leads to interoperability defects, so it is
strongly recommended that implementations do not follow it.

And from http://unicode.org/faq/char_combmark.html#19

Q: Is it possible to apply a diacritic or combining enclosing mark to a sequence of more than one (non-combining) character?

A: No, with the exception of the “double diacritics” deliberately designed to be applied onto a two letter sequence, e.g. U+035D COMBINING DOUBLE BREVE. Neither ZWJ (U+200D ZERO WITDH JOINER) nor CGJ (U+034F COMBINING GRAPHEME JOINER) “glue” characters together in a way that the scope of any following combining character would be affected. To get a character sequence like “Esc” into something like the U+20E3 COMBINING ENCLOSING KEYCAP, you must resort to higher-level protocols. [KP]