docs: function parseExpression() {
          var expr, startToken = lookahead, expressions;
  
          expr = isolateCoverGrammar(parseAssignmentExpression);
  
          if (match(',')) {
              expressions = [expr];
  
              while (startIndex < length) {
                  if (!match(',')) {
                      break;
                  }
                  lex();
                  expressions.push(isolateCoverGrammar(parseAssignmentExpression));
              }
  
              expr = new WrappingNode(startToken).finishSequenceExpression(expressions);
          }
  
          return expr;
      }