The following post may be relevant to whether or not to use Private Use Area mappings for the ligature glyphs.
The glyphnames.dat file can be opened in WordPad.
Near the end of the file there are some ligatures indicated and they all have code points, though those are the code points for the ligatures that have regular Unicode code points.
Erwin is intending to go into more detail tomorrow. At the moment it is not clear to me whether adding a ligature to that list would require a code point.
I did notice from the glyphnames.dat file that, with a few exceptions, the preferred format for a postscript name for a ligature is to include the underscore character, though that appears to be optional.
quote
FB03;f_f_i;preferred
FB03;ffi
end quote
So, although I was intending to use da, de, do etc as postscript names for the ligature glyphs in a blackletter font, I am now wondering whether d_a, d_e, d_o would be better.
Something I need to test is whether the Serif PagePlus X5 program makes any presumptions regarding the name for the ffi ligature.
As my list of blackletter ligatures does have a number with long s in them and some with long s followed by long s I am thinking that using an underscore would be better.
quote
FB05;longs_t;preferred
FB05;longst
end quote
It might come down to personal choice, yet if the glyphnames.dat file has ligatures added into it, it would perhaps become helpful to a user of FontCreator to be using the same list as other people using FontCreator.
I am awaiting the details from Erwin with interest.
William Overington
20 May 2013