It applies element-wise across both arrays. What you're describing is more like an each-right (+/:) or each-left (+\:).
2019-09-25 14:44:44 2core 3gb avx2 © shakti l test
v:3 4
v+v
6 8
v+'v
6 8
+'[v;v]
6 8
v+/:v
6 7
7 8
+/:[v;v]
6 7
7 8
> v+'v /v plus EACH v, i.e. (3+3;4+4).
> 6 8
How is for EACH working here? Adding v (a 2-vector) to each element gives a 2-vector, so why isn't the result a 2-vector of 2-vectors?