def METHOD_NAME(self) -> None:
    """Process a diff range line."""
    match = re.search(r'^@@ -((?P<old_start>[0-9]+),)?(?P<old_count>[0-9]+) \+((?P<new_start>[0-9]+),)?(?P<new_count>[0-9]+) @@', self.line)
    if not match:
        raise Exception('Unexpected diff range line.')
    self.file.old.set_start(int(match.group('old_start') or 1), int(match.group('old_count')))
    self.file.new.set_start(int(match.group('new_start') or 1), int(match.group('new_count')))
    self.action = self.process_content