Just a followup to my own posting: i fixed three bugs in util::html_diff (see commit log http://cvs.openacs.org/cvs/openacs-4/packages/acs-tcl/tcl/util-diff-procs.tcl?view=log) and commited to CVS HEAD. For some random examples, the output seems now quite ok. I'll add some optional support to xowiki to use it.

However, i noticed that tagging of acs-tcl/tcl/util-diff-procs.tcl is unusual/strange/wrong. Although this file is in CVS HEAD, it is tagged with openacs-5-4-compat; as a consequence, it does not show up in a checkout with tag oacs-5-4, but it will be contained in "install/update" from repository. Not sure, who has tagged it with which intentions. Maybe the goal was to include it in oacs-5-4?