Update:
I did some research and found out that the code is really old, it was entered by fixing e1d0a1479and saved more or less since then it has not changed. (2003/04/10)
The author of this code was Wez Furlong. I would ask him, since I am afraid that no one will be able to give a better answer. (Find your email address on github )
IMHO ( atm), , .
stream_context_set_params(): notification ( ) ( ) options, - , stream_context_set_options().
, stream_context_set_params() , atm. .