Hmm... would it be possible to convert the list to something that allows multiple selections...
In a sense this is easy to do by adding a 'multiple' attribute to the <select> tag, but this interface is not very good. Maybe we should create our own type of control which is some kind of dropdown with checkboxes.
In addition alternatives to display or exclude items with a null value would be useful.
null value
<>null value
The null/not null support is not related to this and is moved to a separate ticket #964.
