As much as I hate to say it, selecting multiple items from a List is generally NOT a good use of a Combo Box type widget -- especially since most trigger a selection instantly after the first item is selected. Is there a reason that this has to be a Combo Box (or Tk::JBrowseEntry to be precise)? I believe that none of the current Tk Combo Box type widgets provide the functionality that you are looking for.

One of the problems is how is the Entry supposed to display the results of a multiple selection? Comma-separated words? What happens if one of the items in the list contains a comma or whatever delimiter you plan on using?

Here are some alternatives:

1. Just use a listbox. It already allows for multiple selection. Do you need user-defined entries? Try using using an entry and a button that adds entries to the Listbox. Too many widgets on Screen? Create a button underneath or above the Listbox that triggers a popup Entry to add a new item to the Listbox (pretty much the reverse of what is typically done with a combo box).


2. Try using a Menu with CheckButtons if the list is fairly small and static.