Square Brackets with Tick

[Richard Wordingham]

On Mon, 24 Aug 2015 11:00:32 +0100 (BST)
William_J_G Overington <wjgo_10009 at btinternet.com> wrote:

> Looking at the document
> http://www.unicode.org/L2/L1999/99159.pdf
> that has been mentioned, the four bracket characters are therein
> described as follows. 

> 4X1F O LEFT BRACKET, REVERSE SOLIDUS TOP CORNER
> 4X20 C RIGHT BRACKET, REVERSE SOLIDUS BOTTOM CORNER
> 4X21 O LEFT BRACKET, SOLIDUS BOTTOM CORNER
> 4X22 C RIGHT BRACKET, SOLIDUS TOP CORNER
> So it looks like the pairings in Unicode today are as originally
> intended.

How so?

There are two relevant pairings in Unicode - the Bidi_Mirroring_Glyph
and Bidi_Paired_Bracket.  Both pair the 1st and the 4th together and
the 2nd and the 3rd together.  Now, Bidi_Mirroring_Glyph is based mainly
on appearance (or have I missed a caveat?), and that seems to be
correct.  Bid_Paired_Bracket is based on semantics, which are
difficult to be sure of when we have no examples of use.  Indeed, some
quote marks are notoriously inconsistent from language to language.

I am assuming that it is better to render reversed ⊄ U+2284 NOT A SUBSET
OF (= <U+2282, U+0338 COMBINING LONG SOLIDUS OVERLAY) using an
unreversed glyph for ⊃⃥ <U+2283 SUPERSET OF, U+20E5 COMBINING REVERSE
SOLIDUS OVERLAY>, rather than the unreversed glyph of ⊅ U+2285 NOT A
SUPERSET OF = <U+2283, U+0338>, despite U+2284 and U+2285 being a
bidi-mirroring pair.  If one took the view that a combining solidus
didn't mirror (as indeed, it doesn't according to the UCD), and that
the ticks are unhidden parts of solidi, then the Bidi_Mirroring_Glyph
properties would be wrong!  Good taste is probably the only way through
the bidi mirroring maze.

Richard.