The Arduino reference mentions reading only, not writing back.
this is a poor C++ reference… don’t use it as a complete source of truth, they take many shortcuts there.
A bit rough to read but this is more like it cv (const and volatile) type qualifiers - cppreference.com
- volatile object - an object whose type is volatile-qualified, or a subobject of a volatile object, or a mutable subobject of a const-volatile object. Every access (read or write operation, member function call, etc.) made through a glvalue expression of volatile-qualified type is treated as a visible side-effect for the purposes of optimization (that is, within a single thread of execution, volatile accesses cannot be optimized out or reordered with another visible side effect that is sequenced-before or sequenced-after the volatile access. This makes volatile objects suitable for communication with a signal handler, but not with another thread of execution, see std::memory_order). Any attempt to refer to a volatile object through a glvalue of non-volatile type (e.g. through a reference or pointer to non-volatile type) results in undefined behavior.