docs: @Pure
  	protected URI computeUnusedUri(ResourceSet resourceSet) {
  		String name = "__synthetic";
  		for (int i = 0; i < Integer.MAX_VALUE; ++i) {
  			URI syntheticUri = URI.createURI(name + i + "." + getScriptFileExtension());
  			if (resourceSet.getResource(syntheticUri, false) == null) {
  				return syntheticUri;
  			}
  		}
  		throw new IllegalStateException();
  	}