There are many files that you usually don't want to have under version
control. That includes editor backups and compiled or otherwise
DARCS:RECORD-CHANGES will not record a file
unless you tell it to, but on the other hand it will ask about all files
that are not yet recorded, which can be annoying.
Thus you can define files and directories matching certain regexps as “boring”, not to be included in patches. The file _darcs/prefs/boring contains such regexps, one per line. Lines starting with # are ignored.
The original darcs client supports choosing another file as the list of boring regexps, and keeping this file under version control in the tree. cl-darcs doesn't yet support that.