The section should cover the following:

• What the API supports:
• Running an internal cross-shard transaction from a mongos.
• Running an internal local transaction on a mongod (in an unsharded or sharded cluster).
• Running an internal cross-shard transaction from a mongod (in a sharded cluster) which acts as the router.
• How to use the API:
• Code references for the use cases above in FLE, WCOS, removeShard etc.
• TransactionRouter/TransactionParticipant yielding and unyielding
• Internal Session Pool