This seems appropriate for something that wants to treat these as ASCII
glyphs with their ambiguous semantics.
This uses the existing apostrophe.curly, and also adds grave.curly (an
alias for quotereversed) and bar.broken (an alias for brokenbar). Of
course there are also 'cvXX' features to enable each one individually as
well.
Unicode takes the position that U+0027 APOSTROPHE is always a straight
apostrophe and is you want a curly one you should use U+2019 RIGHT
SINGLE QUOTATION MARK (or U+02BC MODIFIER LETTER APOSTROPHE but let's
not get into that here). Bedstead generally follows that, putting the
SAA5050 straight apostrophe at U+0027 and the SAA5055 curly one at
U+2019.
Older character standards, though, conflated those two and treated the
difference between them as one of font design. In particular, ETS 300
706: May 1997, "Enhanced Teletext specification" treats position 2/7 as
being the same character in all national sub-sets of the Latin G0
primary set. When coverting Teletext data to Unicode, ZVBI maps 2/7 to
U+0027 whichever national sub-set is in use.
This means that to faithfully display Teletext data in the way that an
SAA5051/2 would, Bedstead needs to interpret U+0027 as a curly
apostrophe. I have accomplished this by adding a new "apostrophe.curly"
alias and including that in the 'ss01' and 'ss02' Stylistic Sets. It
also, of course, gains a new Character Variant feature, 'cv07', so that
you can turn the curly apostrophe on and off independently.
This does cause me to wonder whether there should be a stylistic set to
map U+0020..U+007E onto the SAA5055 glyphs.
The features that generate the variant ocircumflex and ccedilla glyphs
are now treated a being variants of lower-case 'o' and cedilla
respectively. Unlike the SAA5051/2 variants, we don't yet have
variants of their base glyphs. Indeed, for the lower-case 'o' we
probably never will, because the variant is "larger accented versions"
so the unaccented version wouldn't change.
I haven't done anything about the weird SAA5054 ugrave because I'm not
sure there's any real design principle behind it.
I've also added a comment explaining the numbering of 'cvXX' features.
This means that users of this stylesheet can use declarations like
"font-variant: styleset(saa5051)" to request a particular stylistic set.
The separated graphics sets, 'ss14' and 'ss16', are not covered by this
because new applications should use the proper Unicode code points for
separated graphics instead.
This requires choosing a CSS weight for the non-bold versions. I've
gone for 500, matching what we use in the OS/2 table. CSS's default
(and "normal") weight is 400, but the matching rules mean that you'll
get 500 if there isn't a 400 available.
