I'm trying to figure out how to define a slice
that's capable of returning the first element.
>>> x = list(range(100))
>>> s = slice(91, 100, 2)
>>> x[s]
[91, 93, 95, 97, 99] # Highest works fine.
>>> s = slice(10, -1, -2)
>>> x[s]
[] # Nope
>>> s = slice(10, 0, -2)
>>> x[s]
[10, 8, 6, 4, 2] # No zero
>>> 0 in x
True