nl_tokens: Tracks a property if it is not already tracked .
pl_tokens: function track ( property ) { if ( ! ( property in trackedProperties ) ) { trackedProperties [ property ] = <mask> ; values [ property ] = model [ property ] ; Object . defineProperty ( model , property , { get : function ( ) { return values [ property ] ; } , set : function ( value ) { values [ property ] = value ; getListeners ( property ) . forEach ( function ( callback ) { callback ( value ) ; } ) ; } } ) ; } }