code: private ParseTree parseForInStatement(SourcePosition start, ParseTree initializer) {
      eat(TokenType.IN);
      ParseTree collection = parseExpression();
      eat(TokenType.CLOSE_PAREN);
      ParseTree body = parseStatement();
      return new ForInStatementTree(getTreeLocation(start), initializer, collection, body);
    }
docs: 12.6.4 The for-in Statement