chain(config) {
		if (this.parsechain.indexOf(config) == -1)
			this.parsechain.push(config);
	}
Tie another UCI configuration to the map.

By default, a map instance will only load the UCI configuration file
specified in the constructor but sometimes access to values from
further configuration files is required. This function allows for such
use cases by registering further UCI configuration files which are
needed by the map.

@param {string} config
The additional UCI configuration file to tie to the map. If the given
config is in the list of required files already, it will be ignored.