code: function parseRelationalExpression() {
          var expr, previousAllowIn;
  
          previousAllowIn = state.allowIn;
          state.allowIn = true;
  
          expr = parseShiftExpression();
  
          while (match('<') || match('>') || match('<=') || match('>=') || (previousAllowIn && matchKeyword('in')) || matchKeyword('instanceof')) {
              expr = {
                  type: Syntax.BinaryExpression,
                  operator: lex().value,
                  left: expr,
                  right: parseShiftExpression()
              };
          }
  
          state.allowIn = previousAllowIn;
          return expr;
      }
docs: 11.8 Relational Operators