code: function(property, allBindingsAccessor, key, value, checkIfDifferent) {
              if (!property || !ko.isWriteableObservable(property)) {
                  var propWriters = allBindingsAccessor()['_ko_property_writers'];
                  if (propWriters && propWriters[key])
                      propWriters[key](value);
              } else if (!checkIfDifferent || property() !== value) {
                  property(value);
              }
          }
docs: Internal, private KO utility for updating model properties from within bindings property:            If the property being updated is (or might be) an observable, pass it here If it turns out to be a writable observable, it will be written to directly allBindingsAccessor: All bindings in the current execution context. This will be searched for a '_ko_property_writers' property in case you're writing to a non-observable key:                 The key identifying the property to be written. Example: for { hasFocus: myValue }, write to 'myValue' by specifying the key 'hasFocus' value:               The value to be written checkIfDifferent:    If true, and if the property being written is a writable observable, the value will only be written if it is !== existing value on that writable observable