anchor.diff:  
     const _SpecialClassDefinition(
         this.specialClass, this.name, this.libraryName, this.specialFileUri,
  -      {this.required = true, this.packageName = 'Dart'});
  +      {this.required = true});
   
     /// Get the filename for the Dart Library where this [ModelElement]
     /// is declared, or `null` if its URI does not denote a library in
  
positive.code: 
  /// A declaration of a special [Class] and how to find it.
  class _SpecialClassDefinition {
    /// Which specialElement this is.
    final SpecialClass specialClass;
  
  
negative.code:   /// can be found.
    final String libraryName;
  
    /// The URI for the library in which this [ModelElement] is defined.
    final String specialFileUri;
  
  