This system-provided window procedure processes the actions on a prompted entry field (combination-box) control (WC_COMBOBOX).

Purpose

A combination-box consists of an entry field control and a list box control merged into a single control. The list, which is usually limited in size, is displayed below the entry field, and offset one dialog-box unit to its right.

When the combination-box control has the focus, the text in the entry field is given selected emphasis and, if the list box control has a matching entry, it is scrolled to show that match at the top of the list.

A combination-box, while sometimes only showing the entryfield, also owns the area occupied by the invisible list box. Another window can and will be clipped to it if they have clipping flags set.