code: func (r *Route) PathPrefix(tpl string) *Route {
  	r.err = r.addRegexpMatcher(tpl, regexpTypePrefix)
  	return r
  }
docs: // PathPrefix -----------------------------------------------------------------
  // PathPrefix adds a matcher for the URL path prefix. This matches if the given
  // template is a prefix of the full URL path. See Route.Path() for details on
  // the tpl argument.
  //
  // Note that it does not treat slashes specially ("/foobar/" will be matched by
  // the prefix "/foo") so you may want to use a trailing slash here.
  //
  // Also note that the setting of Router.StrictSlash() has no effect on routes
  // with a PathPrefix matcher.