-Returns true if the transaction was submitted successfully, false if
-it failed (or undef if it has not been submitted yet).
+Returns true if the transaction was approved by the gateway, false if
+it was submitted but not approved, or undef if it has not been
+submitted yet.
+
+=head2 partial_auth_amount()
+
+If this transaction was a partial authorization (i.e. successful, but less than
+the requested amount was processed), then the amount processed is returned in
+this field.
+
+(When is_success is true but this field is empty or 0, that indicates a normal
+full authorization for the entire requested amount.)