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 _explicitfiles(kindpats):
    """Returns the potential explicit filenames from the patterns.

    >>> _explicitfiles([(b'path', b'foo/bar', b'')])
    ['foo/bar']
    >>> _explicitfiles([(b'rootfilesin', b'foo/bar', b'')])
    []
    """
    # Keep only the pattern kinds where one can specify filenames (vs only
    # directory names).
    filable = [kp for kp in kindpats if kp[0] not in ("rootfilesin",)]
    return _roots(filable)