function argFlags( alias ) {
	var i;
	for ( i = 0; i < SETTINGS_ALIASES.length; i++ ) {
		if ( SETTINGS_ALIASES[ i ][ 0 ] === alias ) {
			return SETTINGS_ALIASES[ i ].slice( 1 );
		}
	}
	return null;
}
Returns a list of argument completion flags for a specified settings API.

@private
@param {string} alias - alias
@returns {(Array|null)} argument completion flags