What are these variables and where are they documented?

Question

This is in the twentyeleven theme. Can somebody tell me what this is?

<span class="%1$s">Posted in</span> %2$s', 'twentyeleven' )
             ^^^^                   ^^^^

My best googling tells me it's something to do with i18n, but I don't think that's the full story because some of them spit out things like author names and post titles, like this example:

<a class="url fn n" href="%5$s" title="%6$s" rel="author">%7$s</a>
                          ^^^^         ^^^^               ^^^^

At any rate, is this something I can/should be using? What's it actually called, and where is it documented?

Sorry if this is a dumb question, but it's a hard thing to google! Thanks!

Answer 1

See the php sprintf and printf functions. They are tokens that get data from a function or variable separated by commas at the end of the call.

$variable = 'sprintf';
printf( 'Hey dude check out the %s php function', $variable );