In principle I do not object, but this is a preliminary patch. I am
still not happy with the naming of the "check_paths" argument. Also, the
patch was made against the trunk which means that it contains hunks with
the new reStructuredText documentation. Please be patient.

I do not change extract() because it has become more and more a
low-level method over the years, that makes promises it cannot keep and
should not be used at all. I try to discourage its use in the documentation.