Assign F3 as an accelerator key for a menu item called EDIT.ZOOM. This menu option can be visible or hidden. In an MDI frame, the Zoom functionality will operate on the control that has focus in the active window. In a window without an MDI frame, the Zoom functionality will operate on the control that has focus -- the active window is the window containing the menu. The settings, with the menu item visible, are illustrated below:
