Document interfaces that may have methods added in the future

tx.go

@@ -85,6 +85,13 @@ func (c *Conn) BeginTx(ctx context.Context, txOptions TxOptions) (Tx, error) {
 	return &dbTx{conn: c}, nil
 }
 
+// Tx represents a database transaction.
+//
+// Tx is an interface instead of a struct to enable connection pools to be implemented without relying on internal pgx
+// state, to support psuedo-nested transactions with savepoints, and to allow tests to mock transactions. However,
+// adding a method to an interface is technically a breaking change. If new methods are added to Conn it may be
+// desirable to add them to Tx as well. Because of this the Tx interface is partially excluded from semantic version
+// requirements. Methods will not be removed or changed, but new methods may be added.
 type Tx interface {
 	// Begin starts a pseudo nested transaction.
 	Begin(ctx context.Context) (Tx, error)