def flex_loader(alias):
    """
    Loader for L{Flex<pyamf.flex>} framework compatibility classes.

    @raise UnknownClassAlias: Trying to load an unknown Flex compatibility class.
    """
    if not alias.startswith('flex.'):
        return

    try:
        if alias.startswith('flex.messaging.messages'):
            import pyamf.flex.messaging
        elif alias.startswith('flex.messaging.io'):
            import pyamf.flex
        elif alias.startswith('flex.data.messages'):
            import pyamf.flex.data

        return CLASS_CACHE[alias]
    except KeyError:
        raise UnknownClassAlias(alias)