anchor.diff:    /// can be found.
     final String libraryName;
   
  -  /// The package name in which this [ModelElement] can be found.
  -  final String packageName;
  -
     /// The URI for the library in which this [ModelElement] is defined.
     final String specialFileUri;
   
  
positive.code: 
  /// A declaration of a special [Class] and how to find it.
  class _SpecialClassDefinition {
    /// Which specialElement this is.
    final SpecialClass specialClass;
  
  
negative.code: 
    const _SpecialClassDefinition(
        this.specialClass, this.name, this.libraryName, this.specialFileUri,
        {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
  