The horde_text_filter_csstidy:: class provides the php-based library needed to perform optimization/compression on css code. it is provided in a separate package as the code is under the gplv2 license instead of the lgplv2 license used for the text_filter class. this package is part of horde, a web application framework written in php with modules like imp (webmail), turba (contacts), kronolith (calendar), nag (task list), gollem (file manager), etc.