rmnka447, on 2017-August-01, 17:17, said:
If it's forcing, then after 3 ♦, a further ♥ rebid ought to show a hand that's something like 6-4 in the reds and is better than a simple 3 ♥ rebid.
If it's a just preference, then you have to have some way of showing extras and that would probably be double unless you specifically agree on something else.
This bidding situation is the kind of thing that you work out as you develop a partnership. I'm not sure there are any right or wrong answers, just what you agree with your partner and what works for you as a pair.
3♦ I suspect is just competing the partscore.