Feature summary (what you would like to be able to do and where):
Allow for adding an initial set of MenuItems to a Lookup that is shown when the Lookup input receives focus before the user types anything.

Use case:
On Wikidata, when adding a new Property, an extension called "PropertySuggester" is used to suggest an initial set of Properties to add based on the already existing Data for that Entity. This happens when the property selector widget is focused, before the first character is typed.

Benefits:
It would be nice to be able to add initial menu items in a straightforward way.