Mike Walsh

phpHtmllib is a set of PHP classes and library functions to help facilitate building, debugging, 
and rendering of XML, HTML, XHTML, WAP/WML Documents, and SVG (Scalable Vector Graphics) images 
as well as complex html ‘widgets’. It provides a mechanism to output perfectly indented/readable 
tags, and a programmatic API to generating tags on the fly.
More information can be found on the <a href="http://michaelwalsh.org/wordpress/wordpress-plugins/phphtmllib/" rel="nofollow ugc">phpHtmlLib</a> 
plugin page.

phpHtmlLib

The phpHtmlLib library contains a set of PHP classes and library functions to help facilitate…

Roland Rust

It functions as a frontend for the Markup Validator Web Service API on http://validator.w3.org. Stylesheets are checked as well.
Languages available: 
+ english 
+ deutsch(german)

Batch Validator

This plugin performs a batch markup validation check over your entire WordPress website.

phpHtmlLib vs Batch Validator