The package provides an object oriented interface to communicate with W3C's HTML validator by using their XML-based output interface. See the examples page for information on how to use this package to get validation results.
The Services_W3C_HTMLValidator package can be installed using the PEAR installer command pear install Services_W3C_HTMLValidator. If the installation fails due to missing dependencies, one either needs to install them manually or can make the installer fetch all dependencies automatically: pear install -a Services_W3C_HTMLValidator.