Serene is a validation engine that implements the JAXP 1.3 Validation Framework API for RELAX NG based on an algorithm centered on providing good messages and having a clear handling of ambiguity and conflicts. It has an implementation of the JAXP Validation Framework API for ISO Schematron and support for Schematron markup embedded in RELAX NG schemas.
HTML::FormFu is a framework for HTML forms. It aims to be as easy as possible to use for basic Web forms, but with the power and flexibility to do anything else you might want to do (as long as it involves forms). You can configure almost any part of formfu's behavior and output. By default, formfu renders "XHTML 1.0 Strict" compliant markup, with as little extra markup as possible, but with sufficient CSS class names to allow for a wide range of output styles to be generated by changing only the CSS.