Sequence and String
A
1 [a,2,[b,4]]
2
'a,2,[b,4]
3
=A1.string@q(",")
4
=A1.string(",")
5
=A2.array@p(",")
6
=A2.array(",")
7
=A2.array@1(",")

Of A3~A7 the computation results are as follows:

Among the results, the member in blue is a sequence for you to double click and view.