},

        changed: function(bool) {

            if(arguments.length == 0) return this.__changed__;

            this.__changed__ = bool;

            // propagate changed flag upwards

            if(this.parentConstraintVariable && this.parentConstraintVariable instanceof LayoutConstraintVariable) {

                this.parentConstraintVariable.changed(bool)

            }

        },

        child: function(ivarname, child) {

            if(arguments.length < 2)

                return this.__children__[ivarname];

            this.__children__[ivarname] = child;

            child.parentConstraintVariable = this;

        },

        

        // create a ConstrainedVariable for the property given by ivarname

        constrainProperty: function(ivarname) {

            var extentConstrainedVariable = ConstrainedVariable.newConstraintVariableFor(this.value, ivarname, this.__cvar__);

            if (Constraint.current) {

                extentConstrainedVariable.ensureExternalVariableFor(Constraint.current.solver);

                extentConstrainedVariable.addToConstraint(Constraint.current);

            }

            var childConstraintVariable = extentConstrainedVariable.externalVariables(this.solver);

            this.child(ivarname, childConstraintVariable);

            //console.log("FOOOOOO", ivarname, childConstraintVariable, this, childConstraintVariable.parentConstraintVariable);

            return extentConstrainedVariable;