I agree that a developer should and would prefer the `Py_TPFLAGS_*` but when you visit https://docs.python.org/3/c-api/sequence.html
It seems like the best practice to determine Sequence protocol is by using this function, hence leading to confusion. There's no recommendation to use the new `Py_TPFLAGS_*`.
To have this knowledge of `Py_TPFLAGS_*` one should be very knowledgable in Python's C-API.
How about adding a deprecation note to `PyMapping_Check` & `PySequence_Check` in the documentation, suggesting the alternative path (to use `PyType_HasFeature`)?