diff --git a/man/os-release.xml b/man/os-release.xml
index 674180679b5..5a0cfd2887c 100644
--- a/man/os-release.xml
+++ b/man/os-release.xml
@@ -317,6 +317,17 @@
+
+ SYSEXT_LEVEL=
+
+ A lower-case string (mostly numeric, no spaces or other characters outside of 0–9,
+ a–z, ".", "_" and "-") identifying the operating system extensions support level, to indicate which
+ extension images are supported (See:
+ systemd-sysext8).
+ Example: SYSEXT_LEVEL=2 or
+ SYSEXT_LEVEL=15.14.
+
+
If you are reading this file from C code or a shell script