diff --git a/dataformat/upgrade.txt b/dataformat/upgrade.txt
index bfd29d1c945..620e83a2da2 100644
--- a/dataformat/upgrade.txt
+++ b/dataformat/upgrade.txt
@@ -1,7 +1,14 @@
 This files describes API changes in /dataformat/ download system,
 information provided here is intended especially for developers.
 
+=== 3.4 ===
+
+* In order to allow multiple sheets in an exported file the functions write_header() and write_footer() have
+  been removed from core dataformats plugins and have been replaced.
+  - write_header() has been split into the two functions start_output() and start_sheet().
+  - write_footer() has been split into the two functions close_output() and close_sheet().
+  For backwards compatibility write_header() and write_footer() will continue to work but if used will
+  trigger the function error_log().
+
 === 3.1 ===
 * Added new plugin system with low memory support for csv, ods, xls and json
-
-