anchor.diff:    /// parameter.
     bool get isOptionalPositional;
   
  -  /// Return `true` if this parameter is a positional parameter. Positional
  -  /// parameters can either be required or optional.
  +  /// Return `true` if this parameter is a positional parameter.
  +  ///
  +  /// Positional parameters can either be required or optional.
     bool get isPositional;
   
  -  /// Return `true` if this parameter is a required parameter. Required
  -  /// parameters can either be positional or named.
  +  /// Return `true` if this parameter is a required parameter.
  +  ///
  +  /// Required parameters can either be positional or named.
     ///
     /// Note: this will return `false` for a named parameter that is annotated
     /// with the `@required` annotation.
  
positive.code:   /// ('import', 'export', 'library' or 'part') to the given [token].
    void set keyword(Token token);
  
    /// Return the source that was selected based on the declared variables. This
    /// will be the source from the first configuration whose condition is true,
    /// or the [uriSource] if either there are no configurations or if there are
    /// no configurations whose condition is true.
    Source get selectedSource;
  
    /// Return the content of the URI that was selected based on the declared
    /// variables. This will be the URI from the first configuration whose
    /// condition is true, or the [uriContent] if either there are no
    /// configurations or if there are no configurations whose condition is true.
    String get selectedUriContent;
  
    /// Return the semicolon terminating the directive.
  
negative.code:   void set uriSource(Source source);
  }
  
  /// An identifier that has an initial value associated with it.
  ///
  /// Instances of this class are always children of the class
  /// [VariableDeclarationList].
  ///
  ///    variableDeclaration ::=
  ///        [SimpleIdentifier] ('=' [Expression])?
  ///
  /// Clients may not extend, implement or mix-in this class.
  // TODO(paulberry): the grammar does not allow metadata to be associated with a
  // VariableDeclaration, and currently we don't record comments for it either.
  // Consider changing the class hierarchy so that [VariableDeclaration] does not
  // extend [Declaration].
  abstract class VariableDeclaration implements Declaration {
    @override
    VariableElement get declaredElement;
  