+Beyond PreProcessorDirectives, Other types of hooks that can be used by
+plugins include:
+
+### checkconfig
+
+ IkiWiki::hook(type => "checkconfig", id => "foo", call => \&checkconfig);
+
+This is useful if the plugin needs to check for, or modify ikiwiki's
+configuration. It's called early in the ikiwiki startup process. The
+function is passed no values. It's ok for the function to call
+IkiWiki::error if something isn't configured right.
+
+### filter
+
+ IkiWiki::hook(type => "filter", id => "foo", call => \&filter);
+
+Runs on the raw source of a page, before anything else touches it, and can
+make arbitrary changes. The function is passed named parameters `page` and
+`content` should return the filtered content.