iptables does not have a useful manpage, describing all modules and their targets. See, for example, the corresponding Debian package. iptables package version 1.4.18
Use man iptables-extensions. This is described in the iptables man page.
Alright, sorry for the noise then, I feel like this bug can be closed. It'd be lovely, though, if the "go to iptables-extensions manpage for the usual stuff" was noted more prominently. The reason I'm suggesting this is stemming from how I came to miss these actually not-that-obscure references. When you use a certain utility for a _long_ time, you learn its documentation ins and outs -- and you switch from the "parse the document" mode to a "grep the document for well-known keywords" mode. And the grep thing totally failed me, indeed. So, I think, a bigger, louder "the structure of this document has changed in significant ways" disclaimer at the start of the manpage would be helpful for lost souls like me..
Closing as "NOT A BUG". BTW: iptables-extensions is referenced in "MATCH AND TARGET EXTENSIONS" and also in "SEE ALSO".