<td colspan=2> no go

1. Amaya 8.7 (on WinXP) doesn't recognize the colspan
attribute for tag <td> or for <th> for doctype xhtml
1.1 ("parse error"), but doesn't have a problem with
it when i save the document as html. So is colspan not
legal in xhtml?  If yes, why?  (And why does it seem
that most commentators (e.g.,
http://www.codeproject.com/html/htmltoxhtml.asp) do
not mention the loss of functionality involved in
going to xhtml from html?)

2. The Change to 4.01 transitional command off of the
File menu didn't work for me. The command seemed to be
ignored by Amaya.

3. I wasn't able to simply close Amaya once the
above-mentioned parse error was found (but I didn't
test closing after attempting to fix the parse error.)

thanks,
george