Sets the default interface that PyAMF will use to deal with XML entities
    (both objects and blobs).

def set_default_interface(etree):
    """
    Sets the default interface that PyAMF will use to deal with XML entities
    (both objects and blobs).
    """
    global types, ET, modules

    t = _get_etree_type(etree)

    _types = set(types or [])
    _types.update([t])

    types = tuple(_types)

    modules[t] = etree

    old, ET = ET, etree

    return old