The Startup Manager website is entirely w3c valid

All the stylesheets are css 2.1 (and 3.0) valid

Valide CSS! Valide CSS! Valide CSS! Valide CSS! Valide CSS! Valide CSS! Valide CSS! Valide CSS!

All the html documents are xhtml 1.1 valid

Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1 Valid XHTML 1.1
And all posts, archive pages and the search form are xhtml 1.1 valid too.

And so is this webpage

Valid XHTML 1.1

The syndication formats provided are valid too

[Valid RSS 2.0] [Valid RSS 2.0] [Valid RSS .92] [Valid RSS .92] [Valid Atom 1.0] [Valid Atom 1.0]

References

W3C logo