Geoffrey Thomas wrote:
line across th for voiced and no line for unvoiced. This last one is the only thing not representable in Unicode;
Not so. Even 8859-1 makes this accomodation because of its need to be compatible with a modern Western language, i.e. Icelandic. Thus #0240 is "ð" (voiced) and #0254 is "þ" (unvoiced). To enter these in an e-mail I simply type the number (with its leading zero) while holding the Alt key.
Ec