enable-clash-detection

I just tried helping somebody compile XEmacs 20.4 to enable clash detection again. So here are a few questions 1. Where is is this documented? 2. Is the default (disabled) intentional? Jan P.S. That 'somebody' also asked me to forward his plea to enable it again. Which I just did :-). However if the answer to 2. is yes (like I think it is because the old clash detection is ugly), I would say we should implement the FSF 20.x style clash detection before reenabling it. I also vaguely remember Steve writing something to that effect. Personally I think locking like this has no place in an application (other than automatic handling of other systems like for CVS).