UK Cabinet office recommends mod_tidy: As part of a study for e-government in the European Union, the UK Cabinet office recommends automated, server-side tools, namely mod_tidy, to gain best quality web documents which are able to pass validation tests and accessibility checks:
[..] As noted, there is a particular role here for procurement policy. It is likely that an explicit requirement to adhere to standards on any web content development or authoring systems, built into procurement documents, and suitably verified, would have a significant impact in driving the improvement of conformance with formal standards in these technologies. In the shorter term, useful progress may be made by deploying server-side systems dynamically to coerce HTML to conform with standards as it is being served (see, for example, the mod_tidy module for the Apache web server at http://mod-tidy.sourceforge.net/) [External website]. In addition, automated tools are available to test the validity of (X)HTML CSS and other formats used. [..]
Detailed information of this (in the meantime archived) study are public available at the Cabinet's online archive with the document eAccessibility of public sector services in the European Union, Section 4 – Detailed analysis of results and with the appropriate PDF document.