This issue was raised at the last conf call and it was agreed to keep discuss, so I'm writing down here.
In the current draft #5, Tr is defined as below:
Tr indicates a possible fallback using the code chart glyph rotated 90 degrees clockwise
Most code points that are assigned Tr were moved from SB in draft #3:
SB brackets which are displayed sideways
I understand that this isn't exactly the scope of UTR#50, but in CSS, some implementers raised concern that it is not easy to change the orientations by using information in the font, and therefore CSS is likely to interpret Tr as U, and assumes font vendors will implement appropriate glyphs in their fonts. I guess there could be more software that has similar limitations and follow the CSS way to interpret Tr, so I would appreciate if UTR#50 can take such possibility into account when assigning Tr value.
I looked into which code points have actual vert glyphs, and here's a table:http://wiki.csswg.org/spec/utr50/vert20120606#tr
I can classify each code point to 3 categories:
- All fonts have V glyphs, so any implementation will be interoperable.
- Some fonts have/lack V glyphs, but since transformation is highly important for the code point that making it Tr is more important than interoperability with such implementations.
- Some fonts have/lack V glyphs, and transformation is almost just rotation. Giving them R makes more interoperable implementations.
From the code points that are assigned Tr as of draft #5 + Consolidated feedback, rev 5, here's my observations:
3008..3019 Category 1.
301A..301B Meiryo doesn't have vert, but all others have. I'd say category 1.
301C Category 2 (Mirroring is required in addition to rotation).
301D..301F We reommend Tu for this; the discussion is in separate topic.
3030 Category 2 (Mirroring is required in addition to rotation.)
30A0 Category 1
30FC Category 2 (Shape tweaking is required in addition to rotation).
FE59..FE5E Category 3. I recommend R for these code points.
FF08..FF09 Category 1
FF1A..FF1B Category 2 (Chinese wants Tu, Japanese wants Tr.)
FF3B Category 1
FF3D Category 1
FF3F Category 1 or 3 (two Chinese fonts lack vert, is it important enough?)
FF5B Category 1
FF5C Category 1 or 3 (one Japanese and three Chinese out of tne fonts lack vert, is it important enough?)
FF5D Category 1
FF5E Category 2 (Mirroring is required in addition to rotation.)
FF5F..FF60 Category 1 or 3 (two Chinese fonts lack vert, is it important enough?)
FFE3 Category 1 or 3 (three Chinese fonts lack vert, is it important enough?)
So, within where we assign Tr today:
- FE59..FE5E are better to be R if we take such implemetations into account
- There are some code points that need discussions. I'm ok for all of them being Tr.