The C++11 is still common enough that if you want a large usage group it's the target. However, it's parsing to a DOM and doesn't use features like PMR, so the language features needed won't be more than std containers and stuff.
But to be honest, I have not yet played around with PMR.
For example, C++/WinRT is a C++17 library, yet plenty of samples use C style strings and vectors.