William Overington wrote: > Also, perhaps there could be a method for asking a font to > please display all its ZWJ sequences and their results. [...] > Now it might be that some advanced font formats can do such things, I > do not know at present. [...] > Also, perhaps some method of asking a font to declare a > list of the code points for which it has a specific glyph would be > helpful. Again, perhaps some advanced font formats have these > abilities, I do not know at present.
A font is not a program that executes machine code. A font is data, and a program only in the sense that, e.g, a PostScript font contains data in the PostScript programming language. Hence, a font can't 'do' this, only an application using the font can. Such an application will extract information it is interested in from the font, and do with it as its purpose commands. A font viewer application might display to the user tables of all glyphs, ligatures, and variations; the information (at least that about the total glyphs) is there in the font by definition. Similarly, it's a matter of the rendering engine to notify the application that requested the rendition (and thereby the user) that it didn't find all the glyphs it was looking for in the font. Maybe neither Unicode nor the font format specifications require such a behaviour, but one could of course write a rendering engine that exhibits it, whatever fonts it works on. Cheers, Thomas -- Thomas Lotze thomas.lotze at gmx.net http://www.thomas-lotze.de/
