anchor.diff:  /// Clients may not extend, implement or mix-in this class.
   @experimental
   abstract class ClassOrAugmentationElement
  -    implements InterfaceDefiningOrAugmentationElement {
  +    implements InterfaceOrAugmentationElement {
     /// The immediate augmentation of this element, or `null` if there are no
     /// augmentations. [ClassAugmentationElement.augmentationTarget] is the back
     /// pointer that will point at this element.
  
positive.code: /// Clients may not extend, implement or mix-in this class.
  @experimental
  abstract class MixinOrAugmentationElement
      implements InterfaceDefiningOrAugmentationElement {
    /// The immediate augmentation of this element, or `null` if there are no
    /// augmentations. [MixinAugmentationElement.augmentationTarget] is the back
    /// pointer that will point at this element.
  
negative.code:   });
  }
  
  /// Shared interface between [InterfaceElement] and augmentations.
  ///
  /// Augmentations of [InterfaceElement] don't have their own type,
  /// so they cannot by instantiated into an [InterfaceType].
  ///
  /// Clients may not extend, implement or mix-in this class.
  abstract class InterfaceOrAugmentationElement
      implements TypeParameterizedElement {
    /// Return a list containing all of the accessors (getters and setters)
    /// declared in this class.
  