code: @Deprecated
      @RestrictedSince("1.651.2 / 2.TODO")
      @Restricted(NoExternalUse.class)
      public static boolean isAbsoluteUri(@Nonnull String uri) {
          int idx = uri.indexOf(':');
          if (idx<0)  return false;   // no ':'. can't be absolute
  
          // #, ?, and / must not be before ':'
          return idx<_indexOf(uri, '#') && idx<_indexOf(uri,'?') && idx<_indexOf(uri,'/');
      }
docs: Return true if the systemId denotes an absolute URI .
  
  The same algorithm can be seen in {@link URI}, but
  implementing this by ourselves allow it to be more lenient about
  escaping of URI.
  
  @deprecated Use {@code isAbsoluteOrSchemeRelativeUri} instead if your goal is to prevent open redirects