Why would you want this? I'm not understanding the use case here...

angus wrote:

One use case:

In Spanish Wikipedia we put a sign on subpages in namespaces User and User talk, because some users prepare their articles there, and some visitors confuse them with legit articles.

This is the rule in Common.css:

body.ns-2 div#contentSub > span.subpages:before,
body.ns-3 div#contentSub > span.subpages:before {

content: " ¡Atención! Este no es un artículo enciclopédico, sino un espacio de trabajo personal. ";
/* etc.. */

}

But this fails if, for example, the page is User:X/Draft, but User:X doesn't exist.