Add more explicit documentation to OpaqueTableStorage

State that the transaction object is only needed if
a database is not going to roll back automatically.

python/lsst/daf/butler/registry/interfaces/_opaque.py

@@ -60,8 +60,10 @@ def insert(self, *data: dict, transaction: DatastoreTransaction | None = None) -
             Each additional positional argument is a dictionary that represents
             a single row to be added.
         transaction : `DatastoreTransaction`, optional
-            Transaction object. Can be `None` in some bridges if no rollback
-            is required.
+            Transaction object that can be used to enable an explicit rollback
+            of the insert to be registered. Can be ignored if rollback is
+            handled via a different mechanism, such as by a database. Can be
+            `None` if no external transaction is available.
         """
         raise NotImplementedError()
 

python/lsst/daf/butler/registry/opaque.py

@@ -73,6 +73,8 @@ def __init__(self, *, db: Database, name: str, table: sqlalchemy.schema.Table):
 
     def insert(self, *data: dict, transaction: DatastoreTransaction | None = None) -> None:
         # Docstring inherited from OpaqueTableStorage.
+        # The provided transaction object can be ignored since we rely on
+        # the database itself providing any rollback functionality.
         self._db.insert(self._table, *data)
 
     def fetch(self, **where: Any) -> Iterator[dict]: