Forum OpenACS Development: Re: Bug in xowiki page includelets resolution when viewing live revision
It well established that scripted solutions are slow on large input files (see e.g. the comments on http://esw.w3.org/topic/HtmlDiff). The best free alternative seems to be currently daisydiff from Google code (gsoc project in 2007) and maybe the php implementation for mediawiki based on the same algorithm (gsoc project in 2008) http://code.google.com/p/daisydiff/ . If someone has time, interest and skills, it sounds like a nice little project to compare this in detail with the tcl based html diff and maybe port it to Tcl.