Template:Ns has subpages/doc

Detects whether the current or the given namespace has subpages enabled. Returns "yes" if it does, and an empty string otherwise.

This template can be substituted.

Usage

 * (''main space) →
 * (main space) →
 * (main space) →
 * (''main space) →
 * (main space) →
 * (main space) →

The template recognises namespaces which 'should' have subpages, but currently do not (see bug 18437); that is, pages in Category talk:, Help: and Help talk: namespaces. Full page names can be passed, with the obvious caveat that passing the article Template or Category is... inadvisable...