It's a Private En-route IFR rating... basically, you get yourself a perfectly serviceable IR and take all the discrete parts of it (en-route, holding, approaches etc) and do them as individual units.
For example, someone could hold the en-route part of the rating with NO approaches endorsed on their license, and without knowing how to hold...
As you go, you can add bits in (i.e. NDB approach, VOR approach, and so on) to build up to the full IR capability - each type of approach is a seperate endorsement.
Without an approach endorsed, the Wx has to be route LSALT plus 500 on the last segment. Basic "holding" apparently uses procedure turns off a navaid, or somesuch.
Not sure of any recency requirements, but currency is subject to a biennial check flight. The idea is that Joe Bloggs, PPL, can hold a rating to fly VFR at departure and destination, but IFR between, to stop him from scudrunning in poor Wx... unfortunate if the weatherguesser gets it wrong, though...
There was discussion on the foolishness of all this in Dunnunda and Godzone forum but I can't find the thread (albeit with a brief search), but look on the
CASA website for details/dowloads.