"Adam Lindsay"
I'd like to be able to take advantage of some extended ligatures with my pro fonts, but it seems that if users have to enter the ligatures as \Thligature or whatever, they would be of very limited use.
Adam, make use of the "Virtual Fonts" feature in TeX and the backends. How did you install your fonts? You should have some .vf files for your fonts and you can access the contents of them with vftovp (convert back with vptovf) and just add ligature information. See Knuth's "More fun for Grand Wizards: Virtual Fonts" available on ctan or in Knuth's book "Digital typography". (Hope I got the title of the article right.) Virtual Fonts are real fun to play with! It is (imo) one of the best reason to use TeX :) It is completely transparent to the users, no need to say \Thligature or so. Patrick