The reference is not what I am talking about in general, but an example
General - hg clean is pure evil:
'via Blog this'
Tools such as "hg purge" (or got clean)
have options such as
"remove all unknown files" (hg purge)
"remove unknown and ignored files" (hg purge --all)
Methinks there is a third option needed - not files that you have ignored because they are generated, but files that are skipped over, e.g. because they are controlled by a different version control system.
E.g. -X directory -- often I have a different VCS in the subdirectory, .bzr rather than .hg.
It is dangerous to type in "hg purge --all" in such a situation. E.g. it may delete the .hg/.bzr/.git subdirectories.
This is an example of "splitting": what is a simple action "exclude" from the point opf view of "hg add" is actually two flavors from the point of view of "hg purge".