Some categories require not just the normal piping (such as [[Category:1945
births|Smith, John]]), but manipulation of how the links are presented on the
category page. In the sample I cite above, all aircraft are categorised by
manufacturer except U.S. military aircraft with nicknames. The Consolidated PB3Y and
the R3Y Tradewind, for example, are made by the same company but placed under
different letters. The category tag in for the R3Y could be piped of course
([[Category:Seaplanes and flying boats|Consolidated R3Y Tradewind]]), but a passerby
would be bewildered why an 'R' article was appearing in the 'C' section. Moving the
article to a new title seems like overkill, and violates WP:MOS. The easiest
solution is a kind of uber-pipe, so that [[Category:Seaplanes and flying
boats||Consolidated R3Y Tradewind]] (or whatever syntax is implemented) will cause
the link on the category page to show up as 'Consolidated R3Y Tradewind' instead
of 'R3Y Tradewind'.
My apologies if this isn't explained very well. I spent half an hour writing a good
explanation which promptly got deleted when I entered an invalid keyword.