3-4 point high approach large low extension
This was really not seen as joseki, until very recent times. Now some variations are being worked out, just over the last couple of years.
After , at a has been tried too. After Black may play tenuki: but at b for strong shape of course natural too. The question will be what use Black can make of the solidly-supported low stone .
Another way to play is here, for influence. After Black probably connects at a, allowing White to extend on the top side.