VERIFIED SOLUTION i

MailStream Plus (MSP) - When should Mail.dat Field Code CSM-1109 be populated?

Products affected: MailStream Plus™, all versions, all platforms
The Field Name for CSM-1109 in the Mail.dat Standards is "Parent Container Reference ID"
and the Description is-
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Container ID of the Parent Container in which this Child Container resides, if such relationship exists, blank if no such relationship. Parent Containers may have Parent Containers themselves. This is not prohibited; ex: a carton in a sack upon a pallet.

The Container Id of the Parent Container in which this child container resides; such as a tray on a pallet. Populate field with numeric from Container ID CSM-1006 of parent container's .CSM. If no child/parent relationship exists for this container, then field is blank. Populated ONLY for those child containers linked to a parent container; if container is parent only, then field is blank.

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The purpose of the field to to link trays and sacks (on pallets) to the pallet they are on.  
The only time CSM-1109 will be populated by MailStream Plus™ is when trays or sacks are put onto pallets. 
The CSM-1109 field will *not* be populated in non-palletized mailings, nor for bundles placed directly onto pallets. 

FYI- 
The Mail.dat Standards define the layout and usage of the Mail.dat files.  The USPS along withe the IDEAlliance organization maintains the Standards.  They can be found here-
https://www.idealliance.org/specifications

Note:
In some cases though, the USPS PostalOne! uses modifications of the Standards for USPS purposes. Sometimes you may need to verify the PostalOne! usage of a Mail.dat Field. The way to find the current PostalOne! Technical guide it to go to the USPS site here-

https://postalpro.usps.com
UPDATED:  May 23, 2019