The Xforms Institute has released a free online XForms validator. An interactive, Python-powered validator of XForms documents of all sorts that works with multiple host languages. (This information is in part taken from the O’Reilly book XForms Essentials – used with permission). The Mixed-namespace Checking online tool provides several checks of various contents of XForms documents, including scanning for namespace-related errors, unfortunately commonplace in XML development, performing “lint”-like checks for suspicious, but technically legal code, a check of ID/IDREF connections, even if these aren’t properly DTD-declared, and a Relax NG validation of individual “islands” of XForms content within the host document. There is also an online Document Checker, sample queries, and an XForms Validator Bookmarklet.