+## format
+
+ IkiWiki::hook(type => "format", id => "foo", call => \&format);
+
+The function is passed the complete page content and can reformat it
+and return the new content. The difference between format and sanitize is
+that sanitize only acts on the page body, while format can modify the
+entire html page including the header and footer inserted by ikiwiki, the
+html document type, etc.
+