<kbd><b>{apre href=... [+state -state ...]}</b></kbd>: Adds or removes a prestate
option. Prestate options are simple toggles, and are added to the URL
of the page. Use {if prestate=...} to test for the presence of a
prestate. {apre} works just like the {a href=...} container, but if no
'href' attribute is specified, the current page is used.
