The spec states the performance criteria. The contractor hires an engineer to design that part and submit sealed drawings or calculations.
Common examples are fire sprinkler systems, cold-formed metal framing, metal stairs and curtain wall anchors. Some equipment specs ask for engineered attachment to the structure.
Search your spec section for words such as delegated design, engineered, sealed, stamped and calculations. Engineering costs money and takes time. Get a price from an engineer licensed in the project state before bid day. Put the cost in your bid and allow for the review time in your lead time.