Help: Clarify the usage scope of source_group
I spent a few hours refactoring our code, only to see at the end that it didn't work because of #18856 (closed) (not sure if you want to close this issue with this MR) - so added a hint.
Fixes: #18856 (closed)
Backport: release
Topic-rename: doc-source_group-scope
Edited by Brad King