'Provides all XML documents for that content type
@param document: a Document or subclass object
@param content_type: a MIME content type
@return: list of etree._ElementTree of that content type'

def getTreesFor(self, document, content_type):

    for rel_path in self.overrides[content_type]:
        if (rel_path[0] in ('/', '\\')):
            rel_path = rel_path[1:]
        file_path = os.path.join(document._cache_dir, rel_path)
        (yield etree.parse(utils.xmlFile(file_path, 'rb')))
    return
