Returns the merged configuration data schema for this plugin
        type.

def config_schema(self):
        """Returns the merged configuration data schema for this plugin
        type."""
        from rez.config import _plugin_config_dict
        d = _plugin_config_dict.get(self.type_name, {})

        for name, plugin_class in self.plugin_classes.iteritems():
            if hasattr(plugin_class, "schema_dict") \
                    and plugin_class.schema_dict:
                d_ = {name: plugin_class.schema_dict}
                deep_update(d, d_)
        return dict_to_schema(d, required=True, modifier=expand_system_vars)