Information on Fusion Part ID and _partner_entity_id

As part of the CPQ 25D release, a new field Fusion Part Id has been introduced.

We have a customer who previously had Fusion Products integration enabled, which was later replaced with a third-party system integration. In our existing integrations with ERP, we are using the _partner_entity_id field. However, we could not find any documentation that explains how this field is populated or stored in the backend.

During our testing, we observed that the Fusion Part Id value is being stored in _partner_entity_id. We would like to understand if there is any official documentation that explains this behavior and confirms how this field is populated.