anchor.diff:  
     @override
     void visitForStatement(ForStatement node) {
  -    _recordNodeClass('ForElement (parts)', node.forLoopParts);
       _recordTokenType('ForElement (parts)', node.forLoopParts);
       _recordDataForNode('ForElement (body)', node.body,
           allowedKeywords: statementKeywords);
  
positive.code:       'version': currentVersion,
        'byDistance': byDistance,
        'byElementKind': byElementKind,
        'byNodeClass': byNodeClass,
        'byTokenType': byTokenType,
        'byTypeMatch': byTypeMatch,
      });
  
negative.code:     contextMap[key] = (contextMap[key] ?? 0) + 1;
    }
  
    /// Record information about the distance between recurring tokens.
    void recordTokenStream(int distance) {
      tokenDistances[distance] = (tokenDistances[distance] ?? 0) + 1;
  