Lee>The KindleGen program /may/ require XTHML; I don't know, Mr. Adcock is in a much better position than I to evaluate that question. In any event, requiring XHTML as a master format will certainly have no adverse effects. Well, I can't talk to kindlegen except to say what I have seen it do with things I feed it. First of all, I think you guys are all still thinking "Kindlegen Version 1" whereas the rest of the "dev" world already has moved onto "Kindlegen Version 2". Kindlegen Version 2 outputs a "mobi" file which actually contain two, two, two formats in one. The first format is the old "mobi7" version which everybody knows and loves. The second format "kf8" is basically just epub but Amazon doesn't want to call it epub because they have stuck it inside their own mobi wrapper. But, as mobi_unpack.py demonstrates, one can pop that epub right back out of there. [This is all assuming we are talking about public domain unencrypted mobi content of course. ] So, old crufty Kindles are still effectively "mobi7" devices with all which that means. New Kindles are effectively epub2 machines, with all that means. And Kindles of recent vintage are still running as mobi7 devices but are supposed to be automatically updated to become KF8 "epub2" machines sometime soon. But nobody seems to know which Kindles qualify for updates and which don't. But, in terms of Kindlegen Version 2 which is not what I think PG is running yet, I find I can send it HTML not XHTML and it screams like a banshee over and over again "I cannot take it Captain, she's gunna blow!" but, guess what, a working kf8 file always seems to squirt out the back end. Don't know what happens if you send it really buggy HTML. Kindlegen is supposed to like XHTML 5. And EPUB3 is supposed to like XHTML 5. So, XHTML5 is certainly what I would recommend to anyone who cares about the future. Which, by definition, no one here does.