code: func RegisterAsKnownURL(name, urlRegex string) {
  	compiledRegex := regexp.MustCompile(urlRegex)
  	groupNames := compiledRegex.SubexpNames()
  	knownURLLock.Lock()
  	defer knownURLLock.Unlock()
  	knownURLs[name] = KnownURL{
  		URLRegex:          urlRegex,
  		compiledRegex:     regexp.MustCompile(urlRegex),
  		groupNamesInRegex: groupNames,
  	}
  }
docs: // RegisterAsKnownURL appends to KnownURLs