def addPlugins(self, plugins=(), extraplugins=()):
        """extraplugins are maintained in a separate list and
        re-added by loadPlugins() to prevent their being overwritten
        by plugins added by a subclass of PluginManager
        """
        self._extraplugins = extraplugins
        for plug in iterchain(plugins, extraplugins):
            self.addPlugin(plug)