anchor.diff:    @protected
     void detachChild(Element child);
   
  -  /// This method is the core of the system.
  +  /// Update the given child with the given new configuration.
  +  ///
  +  /// This method is the core of the widgets system.
     ///
     /// It is called each time we are to add, update, or remove a child based on
     /// an updated configuration.
     ///
  -  /// If the child is null, and the newWidget is not null, then we have a new
  -  /// child for which we need to create an Element, configured with newWidget.
  -  ///
  -  /// If the newWidget is null, and the child is not null, then we need to
  +  /// If the `child` is null, and the `newWidget` is not null, then we have a new
  +  /// child for which we need to create an [Element], configured with `newWidget`.
  +  ///
  +  /// If the `newWidget` is null, and the `child` is not null, then we need to
     /// remove it because it no longer has a configuration.
     ///
  -  /// If neither are null, then we need to update the child's configuration to
  -  /// be the new configuration given by newWidget. If newWidget can be given to
  -  /// the existing child, then it is so given. Otherwise, the old child needs
  -  /// to be disposed and a new child created for the new configuration.
  -  ///
  -  /// If both are null, then we don't have a child and won't have a child, so
  -  /// we do nothing.
  -  ///
  -  /// The updateChild() method returns the new child, if it had to create one,
  +  /// If neither are null, then we need to update the `child`'s configuration to
  +  /// be the new configuration given by `newWidget`. If `newWidget` can be given
  +  /// to the existing child (as determined by [Widget.canUpdate]), then it is so
  +  /// given. Otherwise, the old child needs to be disposed and a new child
  +  /// created for the new configuration.
  +  ///
  +  /// If both are null, then we don't have a child and won't have a child, so we
  +  /// do nothing.
  +  ///
  +  /// The [updateChild] method returns the new child, if it had to create one,
     /// or the child that was passed in, if it just had to update the child, or
     /// null, if it removed the child and did not replace it.
     @protected
  
positive.code: /// painting, and hit testing.
  ///
  /// Contrast with [ComponentElement].
  abstract class RenderObjectElement extends BuildableElement {
    /// Creates an element that uses the given widget as its configuration.
    RenderObjectElement(RenderObjectWidget widget) : super(widget);
  
negative.code:     return element;
    }
  
    /// Create an element for the given widget and add it as a child of this
    /// element in the given slot.
    ///
    /// This method is typically called by [updateChild] but can be called
    /// directly by subclasses that need finer-grained control over creating
  