Mandatory resources :
PHP 4.3.0 or newer.
PEAR 1.5.4 or newer.
PEAR::HTML_Common 1.2.4 or newer.
pcre extension.
Optional resources :
PHP 5.0.0 or newer.
PEAR::Services_W3C_CSSValidator 0.1.0 or newer.
PHPUnit 3.2.0 or newer.