combo_boxes and how to use them

I'd like to be able to type a search term into a combo box and, with each typed character, i'd like to perform a SQLite query and get back results that influence what items appear in the popup menu part of the combo-box.  I've been able to do this with a popup_menu and a separate edit_field, but it takes up too much room in the user interface. ideally i'd like to be able to do it from a combo_box.  but there don't seem to be enough hooks into a combo_box to do this. take for example the value parameter.  while a variable bound to it will contain the text typed into the combo_box, it also contains the value of whatever item is pulled down in the popup menu.  this leads to confusion and none of my experiments have been able to get values typed into the combo_box to actually produce new SQLite queries on a character-by-character basis (yes, i tried adding immediate=true to the combo_box instance when i created it).

that said, i'm going to guess that (like everything else in the SDK), there are parameters i can set in a combo_box to deal with the text typed into it and the item selected by the popup separately. i just don't know what they are because they are not mentioned in the documentation for a combo_box.  or i'm wrong and what i am requesting is impossible.  but i thought i'd ask here first.