From @Esanders on Gerrit:
1. There seems to be a timing/debounce bug with the widget: if I type 'user' (all lowercase) fairly quickly then "User" is not highlighted (grey background). If I type slowly everything works as expected.
2. If I press <enter> when nothing is highlighted then (Main) is added to the list. As easy way to reproduce this is to just type "t". If no items are selected, pressing <enter> should do nothing.
3. Pressing backspace next to a selected item/pill converts that namespace back to its namespace number. Given that the widget doesn't expose namespace numbers to the user anywhere else, we should probably try and stick with names.
4. Typing in the namespace number does not show suggestions, but is accepted on return keystroke. This is not a major issue, but my expected behavior would be for the suggestions to show the matching options (e.g. typing `11` will suggest `Template talk`)
* If a user types quickly, the suggestions should still highlight the best match. (There can be a few (micro?) second delay for performance reasons, if needed.)
* If no items are selected in the dropdown, pressing <enter> should do nothing.
* Pressing backspace next to an accepted item/pill should replace the pill with the namespace name, not the number.
* When a user types a number, the correlating namespace name should display in the drop-down suggestions.