I'd like to be able to programmatically open/close the popup of the SplitButton. For example, open it on click of the main button.

How to add a separator item in the SplitButtonItems collection?

The DropDownButton and SplitButton exhibit the following accessibility issues:

• The screen reader cannot read the items in the DropDownButton and SplitButton popup.
• When the DropDownButton is opened with Enter, the user cannot navigate the dropdown items with the arrow keys (tested in NVDA).

This will make it easier to have a dynamic list of options whose order can be preserved.

Otherwise, you need to use conditional markup (which puts newly made visible items at the end), or a @foreach over a descriptor model.