Originally Posted by AlexBell
I used to dabble in website design, and have become quite rigid about the importance of having the HTML validate. ...
"but it was the very best butter"
Validating the HTML by browser standards is somewhat pointless when the issue is conversion to MOBI. You're not displaying this HTML in a browser, but using a tool to build a MOBI file. The HTML must be valid by the standards of the tool you choose to use for the conversion.