code: public function ifMatches(string $param, callable $matcher) : RouteBuilder
      {
          if (!array_key_exists($param, $this->matchers)) {
              $this->matchers[$param] = [];
          }
  
          $this->matchers[$param][] = $matcher;
  
          return $this;
      }
docs: Sets matcher(s) which the given param should match
  for the route to be active.
  
  @param string $param The param name to set the matcher(s) for
  @param callable $matcher The matcher or array of matchers for the param
  @return RouteBuilder
  @throws \InvalidArgumentException