We saw in the previous form example that we can create small user interfaces to enhance the standard form UI. This is also available in documents and spreadsheets, although it is slightly different. I decided to use both of them in this small example to encourage you to experiment and customize more because, even if it takes some time to develop these tools, it is so rewarding from a personal point of view that it's well worth the pain.
UiApp was the first service available in Google Apps Script a few years ago and is still presented as experimental in the documentation, although no announcement has been made (for now) that they will deprecate it in the near future. Google encourages users to switch to an HTML service as this one will continue to be upgraded.
In the meantime, we will continue to show both of them as they both have strengths and weaknesses.
