In this case, it's not that you must conform, but you really ought to try.
I'm getting much better about design standards. With my dhMVCd template, most my pages are XHTML-compliant out-of-the-box. I notice, however, I often fail the CSS tests because the W3C-validator seems to reject style-rule overloading, which I don't quite understand.
Anyway, what I really like are the little "chicklet" images (i.e.,

). Just saw this one:
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Understand the concept, but not quite sure how you earn it.
Here are the W3 Validators:
HTMLCSS