def inspect_varname_prefix(var_name):
    """ Returns the top variable scope name. """
    # empirical
    keywords = "/input_symbol_modality"
    if keywords in var_name:
        return var_name[:var_name.index(keywords)]
    keywords = "/symbol_modality_"
    if keywords in var_name:
        return var_name[:var_name.index(keywords)]
    return None