What version of C++ is used in Bitcoin Core? I can't find the information on which C++ version is being currently used in bitcoin core project?
Is it decided for future releases somehow? How does the situation looks now?
The only thing I could find was Pieter Wuille's comment:

Bitcoin Core is switching to C++11 in the upcoming 0.13 release. Meanwhile, C++14 is already standardized and C++17 is well underway. Stating that Bitcoin Core always uses the latest features seems like a strange statement.

It may look like some XY problem, so the reason I am asking is my GF is long time C++ dev and I am looking for resources to learn C++ to be able to understand bitcoin code. Her first question was which C++ version it's written in, as it supposedly doesn't make sense to learn older versions.
Bitcoin Core:

v0.1.0...v0.12.x: C++03
v0.13.0...v0.21.x: C++11
v22.0...: C++17 (current master branch, no releases yet)