Manual:$wgTidyInternal

Details
Normally you shouldn't need to override the setting except for debugging. To install, use ' ' and add a line ' ' to php.ini.

UPDATE:  just installs the old php4 version (v1.2). The new Tidy2.0 is bundled with PHP5 by default, but is not included in the ubuntu build of PHP5. To install it on Ubuntu 10.04 / PHP 5.2.x:

Add extension=tidy.so to php.ini; set $wgUseTidy=true in LocalSettings.php; finally, restart apache.

--141.30.193.8 20:38, 24 February 2011 (UTC)