I wonder whether
"If<action> is requested by<some_programm>, and
neither<parameter_1> nor<parameter_2> is set, then
<parameter_1> is implied ..."
is correct.
Yes.
I understand that a parameter is required. Not providing the
parameter will result in using a default value. But I don't know
whether to use singular or plural.
I'm afraid I'm not even sure which one would cause you uncertainty -
are you contemplating "<action> are requested", "neither
<parameter_1> nor<parameter_2> are set", or "<parameter_1> are
implied"? The second one is the only one that sounds at all
plausible, and I would still avoid it in writing (just as I would
write "either Sam or Pat is guilty", not "are guilty").