This tag behaves the same way as the [MM_Order_Decision] tag. It is used when you want to nest one decision within another:

[MM_Order_Decision isFree='false']
    [MM_Order_Subdecision isDiscounted='true']
        ...
    [/MM_Order_Subdecision]
    
    ...
[/MM_Order_Decision]

See the [MM_Order_Decision] documentation for details.