L2/15-183

Title: Candidate characters for Grapheme_Cluster_Break=Prepend
Author: Roozbeh Pournader (Google)
Date: July 21, 2015
Action: For consideration by the UTC

UAX #29 Unicode Text Segmentation has been supporting a Prepend class of
characters, presently with no members (it used to contain some Southeast Asian
characters).

The author is proposing that the following characters to be added to the class:

U+0600 ARABIC NUMBER SIGN
U+0601 ARABIC SIGN SANAH
U+0602 ARABIC FOOTNOTE MARKER
U+0603 ARABIC SIGN SAFHA
U+0604 ARABIC SIGN SAMVAT
U+0605 ARABIC NUMBER MARK ABOVE
U+06DD ARABIC END OF AYAH
U+070F SYRIAC ABBREVIATION MARK
U+110BD KAITHI NUMBER SIGN
U+1D173 MUSICAL SYMBOL BEGIN BEAM
U+1D175 MUSICAL SYMBOL BEGIN TIE
U+1D177 MUSICAL SYMBOL BEGIN SLUR
U+1D179 MUSICAL SYMBOL BEGIN PHRASE

Rationale: This is because all the characters above attach to the character or
characters immediately after them in a rather unseparable way (typically
subtending or enclosing them), in a way that there should not be a grapheme
break between them and the character immediately after them. In this way, they
are similar to various combining marks, such as U+20DD COMBINING ENCLOSING
CIRCLE or U+0332 COMBINING LOW LINE that form a grapheme cluster unit with a
base character. The difference is that the base character follows the above 13
characters, instead of preceding them.