anchor.diff:    NamedFunctionElement lookupFunctionElement(Name name) => declaredFunctions[name];
   }
   
  -class BlockElement extends Element with Block {
  +class BlockElement extends Block {
     astElement.Block ast;
     SourceElement sourceElement;
     
  
positive.code:   SourceElement sourceElement;
    
    Name name;
    ClassElement extendsElement = null;
    Identifier get identifier => _decl.name;
    
  
negative.code: /** 
   * Instance of a `ClassElement` is our abstract representation of the class.
   **/
  class ClassElement extends Block implements NamedElement {
    Map<Name, FieldElement> declaredFields = <Name, FieldElement>{};
    Map<Name, MethodElement> declaredMethods = <Name, MethodElement>{};
    Map<Name, ConstructorElement> declaredConstructors = <Name, ConstructorElement>{};
  