Rules 

Description 

Lower numbers appear first (farther left) in the menu.  

For instance, set the GroupIndex property to 0 (zero) for a menu that you always want to appear leftmost, such as a File menu. Similarly, specify a high number (it needn't be in sequence) for a menu that you always want to appear rightmost, such as a Help menu.  

To replace items in the main menu, give items on the child menu the same GroupIndex value.  

This can apply to groupings or to single items. For example, if your main form has an Edit menu item with a GroupIndex value of 1, you can replace it with one or more items from the child form's menu by giving them a GroupIndex value of 1 as well.
Giving multiple items in the child menu the same GroupIndex value keeps their order intact when they merge into the main menu.  

To insert items without replacing items in the main menu, leave room in the numeric range of the main menu's items and "plug in" numbers from the child form.  

For example, number the items in the main menu 0 and 5, and insert items from the child menu by numbering them 1, 2, 3, and 4.