The rationale for documenting it in the porting section is that even though this isn't a guaranteed stable interface, the output *does* potentially affect development tools like Ned's coverage.py, as well as other implementations attempting to adhere closely to CPython's behaviour for any given version.

(Although it doesn't usually help *Ned* much, since he's often the one letting us know that we inadvertently changed some details of the code generator's output...)