I recently upgraded to WordPress 3.1 and was surprised to find that my permalinks had broken. So I did the usual round of plugin testing, first deactivating and then reactivating, but I couldn’t isolate it as a plugin problem.

Then I moved on to testing the permalink settings themselves, checking (and regenerating) the .htaccess file, then testing alternate permalink structures. And I found, essentially, that 3.1 requires a little more tidiness from me.

Previously, my site had run with this Custom Structure, which overrides the native WordPress category archives but did work until the 3.1 upgrade. Under Admin | Settings | Permalinks:

After testing alternate configurations, I found that this structure continues to work in 3.1 without a hitch:

So the issue was my archive system override. (From a usable-URL standpoint, the second structure, /%category%/%postname%/, is cleaner. But it’s disfavored for performance reasons; WordPress documentation indicates that %category% as the first element of a permalink Custom Structure adds database load and slows down the site.)

So providing an alternate Category base, as follows, took care of the problem:

Open source licensing is important — and often overlooked, to the detriment of the community.  In many cases, license provisions are easy to follow, but here’s a puzzle:

This blog runs (1) on WordPress, using (2) Joshua Sowin’s implementation of (3) the Blueprint CSS framework.  Each of these three credits represents an excellent piece of work, but each uses a different open source license: WordPress uses the GPL; Sowin uses Creative Commons; and Blueprint uses a modified MIT license.

Sowin is right to apply his choice of license to his work as derived from Blueprint — the generous terms of the MIT license allow him to do that.

But his work is also derived from WordPress itself, at least arguably: here’s a post arguing that any theme used on WordPress has to be licensed under the GPL, subject to the GPL’s particular permissions and restrictions.  The comments are as interesting as the post itself — exemplary of the confusion that can come into a puzzle like this, and of the stakes involved.

What’s a licensing developer to do?  WordPress provides an answer in a posted legal opinion from the Software Freedom Law Center, but it’s complicated: PHP files have to be GPL’d; other elements don’t.

Not a very clean answer, and one that warrants further discussion here.  Watch for updates as I flesh out this draft discussion.

Meantime, as the grateful user of Sowin’s work, my job is easier to parse  (I don’t think you have to be a lawyer to figure this out): give credit where credit is due.  That’s why, of course, you see each 0f the above three credits in this site’s footer.