It's quite a surprise that some well known websites do not pass through W3C markup or CSS validation.
See:
List of markup validation for common websites
A validation on TSA homepage shows 32 Errors and 8 warnings. (Encoding: Auto detect, Doctype: Auto detect.)
Any ideas?
Validation Services:
W3C Markup Validation Service
W3C CSS Valiation Service
W3C Link Checker