code: public function registerFixer(FixerInterface $fixer, $isCustom)
      {
          $name = $fixer->getName();
  
          if (isset($this->fixersByName[$name])) {
              throw new \UnexpectedValueException(sprintf('Fixer named "%s" is already registered.', $name));
          }
  
          if (!$this->nameValidator->isValid($name, $isCustom)) {
              throw new \UnexpectedValueException(sprintf('Fixer named "%s" has invalid name.', $name));
          }
  
          $this->fixers[] = $fixer;
          $this->fixersByName[$name] = $fixer;
  
          return $this;
      }
docs: @param FixerInterface $fixer
  @param bool           $isCustom
  
  @return $this