code: public com.google.protobuf.ByteString
        getUrlRegexBytes() {
      java.lang.Object ref = urlRegex_;
      if (ref instanceof java.lang.String) {
        com.google.protobuf.ByteString b = 
            com.google.protobuf.ByteString.copyFromUtf8(
                (java.lang.String) ref);
        urlRegex_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
docs: <pre>
  URL prefix. Uses regular expression syntax, which means regexp
  special characters must be escaped, but should not contain groupings.
  All URLs that begin with this prefix are handled by this handler, using the
  portion of the URL after the prefix as part of the file path.
  </pre>
  
  <code>string url_regex = 1;</code>