This widget also has the ability to "remember" the last position of the splitter. This preference can be stored either in the database as a User Preference, or in the user's browser under local storage.
Storing it as a User Preference means that an AJAX call will be made every time the splitter is moved. This preference is user specific and can even be carried accross multiple devices or browsers.
The second possibility is to store the position in the browser's Local Storage. This option does not need to communicate to the database, but it also means that the preference is not user specific and will not be carried to other devices or browsers.
The following splitter region has this option enabled and set to Local Storage. Move the splitter around and remember where you left it. Then refresh the page or create a new session. The last splitter position will be restored on page load.