to save the page to. It's passed a page name, and its type, and returns
the name of the file to create, relative to the srcdir.
-#### `targetpage($$)`
+#### `targetpage($$;$)`
Passed a page and an extension, returns the filename that page will be
rendered to.
+Optionally, a third parameter can be passed, to specify the preferred
+filename of the page. For example, `targetpage("foo", "rss", "feed")`
+will yield something like `foo/feed.rss`.
+
## Miscellaneous
### Internal use pages