The format of preference and session files has changed. LyX 2.0.x is
able to read old files but will save them in the new format.
-The format of layout files has changed but, as before,
-layout2layout.py will convert older versions to the new format
-automatically.
+The format of layout files has changed but, as before, layout2layout.py
+will convert older versions to the new format automatically.
+
+The syntax of the languages file has been changed. If you use a
+modified languages file, you will need to adapt it to the new syntax.
+There has been a large change in how Flex insets are named.
+When exporting back to 1.6.x format user-defined flex insets will not
+be properly reverted. See RELEASE-NOTES for details.
* Upgrading from LyX 1.5.x: