-This function may be overloaded in the derived class for a control with
-{\tt wxLC\_VIRTUAL} style. It should return the index of the items image in the
-controls image list or $-1$ for no image.
+This function must be overloaded in the derived class for a control with
+{\tt wxLC\_VIRTUAL} style having an \helpref{image list}{wxlistctrlsetimagelist}
+(if the control doesn't have an image list, it is not necessary to overload
+ it). It should return the index of the items image in the controls image list
+or $-1$ for no image.