The menu control window procedure responds to this message by inserting the identified item into the menu at the position indicated by the specified MENUITEM data structure (contained within the menu-item structure). If the position is MIT_END, the item is added to the end of the menu. If the style of the item includes MIS_TEXT, the text of the item is specified by pszItemText
The menu control window procedure sets sIndexInserted to the zero-based index of the position of the item within the menu.
Note: It must be sent, not posted, to the menu control.