The corrected diff is sent to standard output. Note that you will probably need to use the -l option when applying the patch, in order to ignore any whitespace differences there may be.
The way this command works is fairly primitive; it boils down to some simple text replacements, followed by an unwrapdiff pass. As a result, all of the limitations that apply to unwrapdiff also apply to dehtmldiff.
Tim Waugh <firstname.lastname@example.org>