If this value is not null, the string contained will be used to Page Backward (Page UP) within the screens presenting a multi-row FieldMap.
If the value is null, the PageBackwardKey for the active TaskProject or UIProject will be used from the generic list class.
Examples:
P[enter]
Will send the "P" key (for "Previous") along with an Enter...for a host that doesn't use PageUp or F7 keys to scroll backward, but instead uses a "function" entry field
[pf9]
Perhaps the normal key is a PF7 and that is setup for the project, but for some reason this list screen was programmed to use a PF9 to page backward through the list...