[pypy-dev] is the handling of python signals a language implementation detail?

[Laura Creighton]

I am reading 18.8.1.1 and 18.8.1.2 in
https://docs.python.org/3/library/signal.html which clearly is written
from the CPython point of view.

....A Python signal handler does not get executed inside the low-level
(C) signal handler. Instead, the low-level signal handler sets a flag
which tells the virtual machine to execute the corresponding Python
signal handler at a later point(for example at the next bytecode
instruction) ... Python signal handlers are always executed in the
main Python thread, even if the signal was received in another thread ...

But is this part of the language definition?  Or an implementation detail?

Laura