nested tables do not copy well

[shriram]

Here's a program:

t = table: parent, sub
  row: "A", 
    table: child
      row: 1 row: 2 row: 3 row: 4
    end
  row: "B",
    table: child
      row: 5 row: 6 row: 7 row: 8
    end
end

fun sum-list(l): for fold(sum from 0, i from l): sum + i end end

transform t using sub:
  parent: sum-list(extract child from sub end)
end

Copying the resulting output produces:

parent	sub
10	child1234
26	child5678

I understand it may be unclear what the exact output should be with nested tables (is that even a thing in T/CSV?), but I don't know if this output is ideal either. Indeed, one can imagine two forms of output, one of which preserves the nesting (which may not be purely T/CSV-compliant, but is still really useful for pasting into chat boxes), and the other of which is more T/CSV-compliant by constructing that uses joins to flatten out the nesting.

One can also imagine "value printing": producing the output as a table value, which can unambiguously be copied.