On Sat, 25 Jul 2015 10:51:19 +0300 Eli Zaretskii <e...@gnu.org> wrote:
> > Reread the Bidi algorithm, especially > > http://www.unicode.org/reports/tr9/#L4 and > > http://www.unicode.org/reports/tr9/#HL6. > > > > In principle, I could have a higher-level protocol that mirrors > > lamedh on Wednesdays, but I must follow the rules for parentheses. > > I don't see how this is related. What HL6 describes is something that > should make sense. For example, Emacs uses '/' as a kind of > "mirrored" '\', when it needs to indicate that a line in an R2L > paragraph is continued on the next screen line. HL6 reads: "Certain characters that do not have the Bidi_Mirrored property can also be depicted by a mirrored glyph in specialized contexts. Such contexts include, but are not limited to, historic scripts and associated punctuation, private-use characters, and characters in mathematical expressions. (See Section 7, Mirroring.) These characters are those that fit at least one of the following conditions: 1) Characters with a resolved directionality of R 2) Characters with a resolved directionality of L and whose bidirectional type is R or AL" The logic of my statement is as follows: a) 'Specialised contexts' is undefined; 'specialised context' may therefore include 'whenever I see fit'. b) The bidirectional type of lamedh is 'R', and it will always have a resolved directionality. The resolved directionalities are 'L' and 'R'. c) Therefore I may choose to mirror all lamedhs on Wednesdays. Similarly, an arrow with a resolved directionality of R may be mirrored if a higher level protocol so dictates. The issue lies with the wording of condition (1). One might expect it to apply only to characters with a bidirectional type of L. That should work for text whose directionality is known when written. It would be interesting to hear the rationale for the wording. My surmise is that it attempts to address text whose directionality is not known before rendering. The most obvious example would be where an application is laying out boustrophedon text in. The author would not be able to correctly choose between COMMA and REVERSED COMMA (an anachronistic example) depending on text direction if line-breaks were not fixed. Richard.
