Best I can tell, the possible values for this aren't documented anywhere.
p[-2*S:-S]
Number of bytes originally asked for. This is a size_t, big-endian (easier
to read in a memory dump).
-p[-S:0]
+p[-S]
+ API ID. See PEP 445. This is a character, but seems undocumented.
+p[-S+1:0]
Copies of FORBIDDENBYTE. Used to catch under- writes and reads.
p[0:N]
The requested memory, filled with copies of CLEANBYTE, used to catch
p[0: S]
Number of bytes originally asked for. This is a size_t, big-endian (easier
to read in a memory dump).
-p[S: 2*S]
+p[S}
+ API ID. See PEP 445. This is a character, but seems undocumented.
+p[S+1: 2*S]
Copies of FORBIDDENBYTE. Used to catch under- writes and reads.
p[2*S: 2*S+n]
The requested memory, filled with copies of CLEANBYTE.