diff --git a/doc/manual.adoc b/doc/manual.adoc
index c03e917..0c2f558 100644
--- a/doc/manual.adoc
+++ b/doc/manual.adoc
@@ -50,6 +50,9 @@ version on start.  newfol does not accept schema files that have a newer version
 than it currently supports, but it ignores directives it does not understand,
 and so can be manually downgraded by editing the `fmt` directive.
 
+Any record beginning with a `#` is ignored as a comment and preserved on
+upgrades.  Extra fields in a record are ignored.
+
 === Configuration File
 
 Configuration files are identical to schema files except that instead of the