Extended slicing and Ellipsis - where are they used?

[Rodney Maxwell]

The following are apparently legal Python syntactically:
   L[1:3, 8:10]
   L[1, ..., 5:-2]

But they don't seem to work on lists:
>>> l = [0,1,2,3]
>>> l[0:2,3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers
>>> l[...]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers

So where is this extended slicing used?

--
Rodney