Added note about EXT_CONTINUE to 3.x -> 4.x migration guide

diff --git a/doc/build/content/intro.txt b/doc/build/content/intro.txt
index 9150f1d4ba53ffbee25549921bd0640f43e96b84..d9882270b205c4d510b280d314e69a9cf87aea4a 100644 (file)
--- a/doc/build/content/intro.txt
+++ b/doc/build/content/intro.txt
@@ -157,4 +157,6 @@ This mostly applies to SQL constructs where you pass a type in:
     
     func.now(type_=DateTime)
     
-    
+### Mapper Extensions must return EXT_CONTINUE to continue execution to the next mapper
+
+If you extend the mapper, the methods in your mapper extension must return EXT_CONTINUE to continue executing additional mappers.