+One good way (if possible) would be to provide a directive like `\[[!sidebar
+id=sidebar]]` which would cause the file, in which it occurred to fill the
+slot `SIDEBAR` in the template: basically, a page `foo.mdwn` says
+`\[[!fillslot slot=myslot]]` and then its contents should go into `<TMPL_VAR
+SLOT_MYSLOT>` for all pages. Ideally, this can then be overridden, so if
+`/bar/foo.mdwn` also references `myslot` then pages under `/bar` should get
+those contents instead.
+