[LRUG] Array.slice question

[Michael Pavling]

I'm just running through the Ruby Koans for a bit of fun, and I've
quickly come upon a case that doesn't make sense to me. I've re-read
the documentation, but I still don't understand why it happens.

Having a play with this array in the console:
  >> x = %w(a b c)
  => ["a", "b", "c"]
  >> x[1]
  => "b"
  >> x[2]
  => "c"
  >> x[3]
  => nil

All makes sense so far, but when I call x[3,0] I *expect* it to return
nil (as the starting index is out of range), but it returns an empty
array:
  >> x[3,0]
  => []

x[4,0] behaves as I expected:
  >> x[4,0]
  => nil

I know it's going to be me not understanding the documentation
properly, but *unless* I can understand it, it's going to leave me
confused. Can anyone explain it simply and clearly, please?

TIA