Template:Documentation subpage/doc

Usage
or: This template should be placed at the top of "/doc" pages. It changes output depending on where it is viewed:
 * On a "/doc" page, it displays a box explaining template documentation and links to the template page.
 * On other pages (ie, pages transcluding the "/doc" page), it notes that the documentation is transcluded from a subpage.

Functions
In addition to the output message, the template categorizes pages to :Category:Documentation subpages|Documentation subpages and defaults the sort key to the page name without namespace (ie, "Foo" on "Template:Foo", so it would be sorted in categories under 'F').