This arose from a conversation on wikien-l.
There is some pretty strange behaviour involving the ISBN "magic word" when used as the label in a piped link.
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In summary, it looks like: * Plain text like "ISBN 123" gets mapped to http://en.wikipedia.org/wiki/Special:Booksources/isbn123 * Plain text with slashes or hyphens or whatever are mapped to different URLs (slashes, fwiw, are mapped to underscores), which all behave identically - extraneous characters are treated as though they're not there http://en.wikipedia.org/wiki/Special:Booksources/isbn1_2-3 * You can access this page via [[Special:Booksources/isbn123]] * When a link to an ISBN page like that is piped via an "ISBN" text, the actual link is ignored, and the piped label is used instead: [[Special:Booksources/isbn123|ISBN 456]] actually links to the ISBN page for 456, and the link reads "ISBN 456".
So far so good? Well, it's odd, but explainable by the "ISBN ..." text being parsed and treated later in the cycle. Now, here's the killer: *[[Test|ISBN 456]] links to Test!
(see the example at http://en.wikipedia.org/wiki/User:Stevage/sandbox )
That's the one I can't understand - putting "ISBN xxx" in the piped part of a link only overrides the actual link if it it's to an ISBN page. This is most unexpected. I suppose it has some strange "prevent misleading ISBN links" benefit, but it's just...odd.
To be honest, the fact that the piped label gets "interpreted" for magic words at all just looks like a bug, or an oversight, or a misfeature or whatever. From some more testing it looks like some "magic word" behaviour gets interpereted in piped links and some doesn't - http:// links *don't* override the actual link for instance.
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Stephen Bain and I were also wondering about the history of the ISBN magic word. When did it appear, what was the reasoning etc? Since it can be implemented perfectly well as a normal template ([[Special:Booksources/isbn{{{1}}}|ISBN {{{1}}}]]), was the decision to make it a magic word just a legacy thing to make thousands of existing ISBN's suddenly "come to life"?
Also, is it documented anywhere? Haven't looked anywhere except http://meta.wikimedia.org/wiki/Help:Magic_words .
Thanks very much, Steve