Creating separate glyphs for pairs of characters is IMO a bad solution: none of these glyphs is present in Unicode, so they have to be implemented in the PUA, where no compatibility can be guaranteed.
Ligatures do not need to be encoded except as underlying characters: glyph substitution lookups should be used to map from, e.g. the letters f and j to an fj ligature. There are, currently, only a handful of applications supporting such substitution, but this is true of many of the more complex aspects of Unicode text rendering. Expect this number of applications to increase significantly over the next couple of years. In the meantime, using PUA codepoints to encode *any* semantic combination of characters is a Really Bad Idea that reduces the life expectancy of your document.
John Hudson
Tiro Typeworks www.tiro.com Vancouver, BC [EMAIL PROTECTED]
It is necessary that by all means and cunning, the cursed owners of books should be persuaded to make them available to us, either by argument or by force. - Michael Apostolis, 1467
