Over here Paul Hunt was asking about how to deal with the Unicode unification of the hooked f and florin as a single character. This strikes me as a build issue, so I'm posting comments here.
In the general case of two possible forms for a single Unicode character you usually need to decide two things:
1. Which form will be the default, i.e. which glyph will be mapped to the Unicode character directly in the cmap table.
2. What method will be used access the second form, i.e. in what layout feature is it appropriate to map the non-default glyph to the default glyph?
The fhook / florin case is a troubling one, though, because there isn't an obvious answer to the second question. Personally, I think it was a really bad unification in Unicode: the florin should have been encoded separately in the currency symbol block. But it is much too late to do anything about that.
I usually make a font-level distinction about this character. If a font has limited language support, e.g. it only supports the Latin 1 character set or one of its derivatives (Mac Roman, MS codepage 1252, etc.) I'll encode a florin symbol glyph a U+0192. If a font supports a wider range of languages, including languages that use the hooked f as a letter, then I'll encode a normal lowercase hooked f glyph at U+0192. The choice can be simplified like this: Does the font contain an uppercase hooked F (U+0191)? If so, then the U+0192 should be the letter not the currency symbol.
It would be possible, in the latter case, to include a special florin currency symbol glyph simply as a stylistic variant, but my inclination would be not to. The straight, lowercase hooked f is recognisable as a florin sign, and there is a risk of ending up with the wrong glyph in text where the hooked f letter is desired, which would be very bad.
A more troubling aspect of the hooked f is that a regular italic f very often has a hooked descender, and is confuseable with the hooked f: f ƒ. So in font families that support languages that use the hooked f as a letter, you need to make a decision about how to design the normal italic f? Do you draw it without a descender? Do you draw it with a straight descender? Do you draw it with a reduced lower terminal? Or do you draw it with the hooked terminal but provide one of the other forms as a stylistic variant for use by people who need to make a distinction with the hooked f?
