concept of an @dfn{active region} exists. The region is active when the
corresponding mark is active. Note that only one active region at a
time can exist -- i.e. only one buffer's region is active at a time.
-@xref{The Mark} for more information about active regions.
+@xref{The Mark}, for more information about active regions.
@defopt zmacs-regions
If non-@code{nil} (the default), active regions are used. @xref{The Mark},