diff --git a/docs/buildsys/koji-cbs.md b/docs/buildsys/koji-cbs.md
index 80e2031..c54a785 100644
--- a/docs/buildsys/koji-cbs.md
+++ b/docs/buildsys/koji-cbs.md
@@ -30,3 +30,24 @@ The proposed and agreed levels are :
   * release: consider stable and tested enough by SIG so ready for public consumption
     * pushed to external mirrors: yes (all mirrors)
     * signed with gpg key: yes
+
+## CBS buildsys tag inheritance
+
+All build targets, depending on distro/release/version, will depend on a `buildsys` tag, that is special and inherited by all SIGs.
+
+The idea is to have some pkgs needed by all builds to be present there and so available by default/inheritance in all tags for the buildroots.
+
+For example, we use [centpkg-minimal](https://git.centos.org/rpms/centpkg-minimal) which contains the needed wrapper script to retrieve automatically sources from the lookaside, and so needed when submitting a build to cbs. 
+Koji will first git clone/pull from upstream git url and then use `get_sources.sh` (from centpkg-minimal pkg, automatically installed in the buildroot) to retrieve source and the rebuild a srpm (a `buildSRPMFromSCM` koji task for every build)
+
+See for example the buildsys9s-release tag, inherited by all SIG tags for CentOS Stream 9 builds : 
+
+```
+cbs list-tagged buildsys9s-release
+Build                                     Tag                   Built by
+----------------------------------------  --------------------  ----------------
+buildsys-macros-el9s-1.0-2.el9            buildsys9s-release    cbs-koji
+centpkg-minimal-2.0.0-3.el9               buildsys9s-release    cbs-koji
+centpkg-minimal-2.0.0-4.el9s              buildsys9s-release    arrfab
+
+```