Page Valet 4 uses mod_validator to deliver the best validator ever! Major performance improvements are coupled with greater accuracy than before (either here or at any other service known to us) and a choice of results formats.
Accessibility Analysis is no longer supported, as this is better accomplished by the companion tool Accessibility Valet.
Why spellcheck? Markup errors are just as ugly and unprofessional as spelling mistakes.
When you publish an invalid webpage, you are relying on error correction in a browser to show your page at all! Another browser may display gibberish, or nothing at all. You may even be breaking the law. More Information.
Page Valet now has catalogue entries for HTML, XHTML, MATHML, SMIL, SVG, WAP/WML doctypes, and DocBook/XML. It should support other document types, but will be slow, as it has to fetch the DTDs over the 'net.
There is no explicit support for non-DTD validation, and any schema used will always be fetched over the 'net.