code: private function handleExponentPart(Context $context)
      {
          // e = %x65 / %x45
          $current = $context->current();
          if ($current !== "e" && $current !== "E") {
              return;
          }
          
          $this->result .= "e";
          $this->isFloat = true;
          $next = $context->next();
          
          // [ minus / plus ]
          if ($next === "+" || $next === "-") {
              $this->result .= $next;
              $context->next();
          }
          
          // 1*DIGIT
          $this->handleFirstDigit($context);
          $this->handleDigitSequence($context);
      }
docs: exp = e [ minus / plus ] 1*DIGIT
  
  @param Context $context