BuilderQ: And that surprises you? microsoft.com claims to be an HTML 4 site (didn't validate that claim though), which could mean it's not XHTML compliant Idem for apple.com. I checked google, and I quickly saw why it was neither valid HTML (any version) or XHTML (due to an unquoted attribute value containing a slash). yahoo.com misses a required attribute for a STYLE element. ibm.com is the only site I didn't spot an error within 10 seconds, and I don't want to bother running it through a validator. But a mistake in its 20k document could be present.