def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def visitdir(self, dir):
        dir = normalizerootdir(dir, "visitdir")
        if not self._m2.visitdir(dir):
            return self._m1.visitdir(dir)

        if self._m2.visitdir(dir) == "all":
            # There's a bug here: If m1 matches file 'dir/file' and m2 excludes
            # 'dir' (recursively), we should still visit 'dir' due to the
            # exception we have for exact matches.
            return False
        return bool(self._m1.visitdir(dir))