The default HTML template is very non-compliant. Generated syntax does not correlate to Doctype DTD. I think it's specified as XHTML 1.1 (which in this case, is more completely insane). You are not supposed to serve XHTML 1.1 as text/html.
For compatibility, and XHTML, serve as
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
This is what Wikipedia does, served as regular text/html. Renders in standards compliance mode and acceptably modern. (should work in ie6)
It would however not be much trouble to use a Doctype
XHTML 1.0 Strict, if your will to do more in regards to syntax.
the major mistakes, considering 1.0 transitional, are..
Not putting quotation marks around attribute values
Incorrect: <td rowspan=3>
Incorrect: <td rowspan='3">
Correct: <td rowspan="3">
Correct: <td rowspan='3'>
Not closing non-empty elements
Incorrect: <p>This is a paragraph.<p>This is another paragraph.
Correct: <p>This is a paragraph.</p><p>This is another paragraph.</p>
there are a few more, but these are the major mistakes.
run a generated page through the w3w html validator, you will see the errors more thoroughly.
this was acceptable for 2000, it was very unacceptable for `09, its now even worse for `11
I'm willing do donate time to fix these issues, just not sure how this project does contributions.
I already created a valid template, but i'ts no good for general use. i removed many features, i was not using. Would not be a big deal to fix the default template, or make a new one.