code: function (binding, cb) {
          if (!this.observedBindings) {
            this.observedBindings = [];
          }
  
          var bindingPath = binding.getPath();
          if (!Util.find(this.observedBindings, function (b) { return b.getPath() === bindingPath; })) {
            this.observedBindings.push(binding);
            setupObservedBindingListener(this, binding);
          }
  
          return cb ? cb(binding.get()) : undefined;
        }
docs: Consider specified binding for changes when rendering. Registering same binding twice has no effect.
  @param {Binding} binding
  @param {Function} [cb] optional callback receiving binding value
  @return {*} undefined if cb argument is ommitted, cb invocation result otherwise