anchor.diff:  /// The result of applying augmentations to a [MixinElement].
   ///
   /// Clients may not extend, implement or mix-in this class.
  -abstract class AugmentedMixinElement extends AugmentedInterfaceDefiningElement {
  +abstract class AugmentedMixinElement extends AugmentedInterfaceElement {
     /// Returns superclass constraints of this element.
     ///
     /// This is a union of constraints declared by the class declaration and
  
positive.code: abstract class ClassElement
      implements
          ClassOrAugmentationElement,
          InterfaceDefiningElement,
          _TmpSharedClassElement {
    /// Returns the result of applying augmentations to this class.
    AugmentedClassElement get augmented;
  
negative.code: /// An element that defines an [InterfaceType].
  ///
  /// Clients may not extend, implement or mix-in this class.
  abstract class InterfaceElement
      implements InterfaceOrAugmentationElement, TypeDefiningElement {
    /// Return a list containing all the supertypes defined for this element and
    /// its supertypes. This includes superclasses, mixins, interfaces, and
    /// superclass constraints.
  