Ivan Detkov: This is (was?) a very popular joseki, especially in handicap games. The cut is a classical hamete. It is a bad move but you better know how to answer.
guile: After reading the comment of strong players here (posetcayand Ivan Detkov). In France, that is a position i saw "treated" in go club a lot of time. It is covered for beginners (sic) in The Nagahara's book "Basic Technique of Go", a very good book with a black cover. I don't find it easy, but it seems to be considered a "basic".
Garouuuh: Is it really possible for 1k players to solve this problem without making multiple mistakes ? Same for problems 43 to 48
guile: If you see this as a Tsumego : NO, you are right.
But it is more a study content, and one fundamental position that player learns when they play high handicap games. As a "study content" it is more around 8k if u consider Go CLub activity.
posetcay: I have never seen this joseki in my life.
Ivan Detkov: I vaguely remember these variants but I am sure I will never play it. One made tenuki already here and E4 is the best answer. E5 looks like an error resulting in a bad ko.
Thanks I.D. and guile!