I use an ErgoDox, and while my layout isn't customized for writing mox invocations, it hadn't occurred to me that this might be a blind spot in my thinking about ergonomics. Good point!
_ is "don't complain because I don't use this variable"
|| is the syntax around Rust closures
foo! is a Rust macro
Why this is desirable is that we can program in real Rust while using some simple macro expansion not to create a free standing language for gui building?
Learning Rust via this gui library might not be the best choice(?) and I think it's better he focus on people that know Rust already.