code: @Internal
  	public <R> SingleOutputStreamOperator<R> process(ProcessWindowFunction<T, R, K, W> function, TypeInformation<R> resultType) {
  		function = input.getExecutionEnvironment().clean(function);
  		return apply(new InternalIterableProcessWindowFunction<>(function), resultType, function);
  	}
docs: Applies the given window function to each window. The window function is called for each
  evaluation of the window for each key individually. The output of the window function is
  interpreted as a regular non-windowed stream.
  
  <p>Note that this function requires that all data in the windows is buffered until the window
  is evaluated, as the function provides no means of incremental aggregation.
  
  @param function The window function.
  @param resultType Type information for the result type of the window function
  @return The data stream that is the result of applying the window function to the window.