docs: function (oldChild, parent, property) {
          var oldChildParents = oldChild ? oldChild[parProp] : null;
          if (oldChildParents) {
              for (var index = 0, parentDescription; parentDescription = oldChildParents[index]; index++) {
                  if (parentDescription.parent == parent && parentDescription.property == property) {
                      oldChildParents.splice(index, 1);
                      // there should be only one.
                      break;
                  }
              }
              if (oldChildParents.length === 0) {
                  __checkAndRemoveBackRefs(oldChild);
              }
          }
      }