Apparently, is a fairly recent Korean development from a dozen years ago.[1] It aims to develop a group on either side of the white kakari (develop on both sides).
White must play hane on top. Next at a or b is normal.
If she plays hane underneath...
White will be pressed low.
[1]
Bill: Actually, it has been around for a while. It appears, with variations, in Suzuki and Kitani's Small Joseki Dictionary, published in 1965.