>>>No, Combobox doesn't have it, only ListBox has.
>>
>>Indeed; now I see it. I was checking the help file for ComboBox, and it included the MultiSelect property - must be the same text for both ListBox and ComboBox.
>>
>>>BTW, what would be a good name for such a listbox class?
>>
>>Something that reflects its function. Since it is supposed to imitate a ComboBox, perhaps ComboMulti or ComboMultiSelect; or, since it is a collapsable ListBox, CollapseListBox, CollapsableListBox, etc.
>
>I coded this class, but I'm thinking I should have used container based class instead of the ListBox as a bare. I don't like some of its current effects :(
>
>In particular, I don't like the gray area at the right side of the listbox. May be I should try adding a button with an arrow at the right side in run-time and only expand it when I click this button.
>
>UPDATE. Yes, I added this - now it looks like a combobox, but it is actually a listbox. Quite a nice class - I may publish it later in my blog.

In theory, it is appropriate to code such classes in a way that hides the internal details (encapsulation); e.g., never access Container.ListBox.... directly, but rather use methods at the container level. If you do this correctly, you can change from a class with container to one without, or change a ComboBox to a ListBox, and you only have to change the single class - not several places where you have used that class.