code: private function _isRedirectRegex ($uri)
  	{
  		// If the URI doesn't look like a regex...
  		if (preg_match('/\/(.*)\/([g|m|i|x|X|s|u|U|A|J|D]+)/m', $uri) === 0)
  		{
  			// Escape all non-escaped `?` not inside parentheses
  			$i = preg_match_all(
  				'/(?<!\\\\)\?(?![^(]*\))/',
  				$uri,
  				$matches,
  				PREG_OFFSET_CAPTURE
  			);
  
  			while ($i--)
  			{
  				$x   = $matches[0][$i][1];
  				$uri = substr_replace($uri, '\?', $x, 1);
  			}
  
  			// Escape all non-escaped `/` not inside parentheses
  			$i = preg_match_all(
  				'/(?<!\\\\)\/(?![^(]*\))/',
  				$uri,
  				$matches,
  				PREG_OFFSET_CAPTURE
  			);
  
  			while ($i--)
  			{
  				$x   = $matches[0][$i][1];
  				$uri = substr_replace($uri, '\/', $x, 1);
  			}
  		}
  
  		// Check if contains a valid regex
  		if (@preg_match($uri, null) === false)
  			$uri = '/^' . $uri . '$/i';
  
  		if (@preg_match($uri, null) !== false)
  			return $uri;
  
  		return false;
  	}
docs: Checks if the redirect URI is a regex
  
  @param string $uri
  
  @return bool|mixed|string