code: func DomainMatcher(pattern string) Matcher {
  	p := pattern
  	if strings.HasPrefix(pattern, ".") {
  		p = pattern[1:] // trim the prefix '.'
  		pattern = "*" + p
  	}
  	return &domainMatcher{
  		pattern: p,
  		glob:    glob.MustCompile(pattern),
  	}
  }
docs: // DomainMatcher creates a Matcher for a specific domain pattern,
  // the pattern can be a plain domain such as 'example.com',
  // a wildcard such as '*.exmaple.com' or a special wildcard '.example.com'.