4-5 point 4-3 approach keima, contact at 6-3
Playing here offers White a simple counter to , in cases where the important ladder is bad for Black.
Black can play confidently at a in cases where the ladder (see below) is favorable. If not, Black at a is somewhat less attractive, and Black will also look at the plays at b and at c.
In this case is what Black wants to play (as a double-purpose move: in order to threaten with a ladder capture while also threatening with isolation by playing at the circled point.
This actual result isn't so common in pro games, since White will try to avoid it.
White will play and assumes the good ladder.
White now has some ladder aji to exploit; Black will complete the capture shortly, and then White will consider expanding the corner at a.
Black is guaranteed good thickness in this line.
If Black has to back down ...
... then this is seen in pro games. is a kind of tesuji based on , because Black doesn't have a good atari play now.
For alternative play by White, see Joseki Dictionary Coverage Depth.
When is played in reply to , is a standard idea, before pushing once more at the circled point (which is after all pushing from behind).
At this point any of a, b or c can be played by Black, according to current pro practice.
This is known only in Korean games. Black is hoping for an improved version of the hanedashi variation.
After these plays it has reached a position from that joseki, but with the / exchange in place. What follows is on similar lines.