Python + strange == cool

[Maboroshi]

All fine and good <below>

 >>> x = ["list1", "list2", "list3", 4, 5, 6, 7]
 >>> x[1:-1]
['list2', 'list3', 4, 5, 6] # All good here

this struck me as weird I had an idea to mess around with lists <below>

 >>> x[1:+1]
[]

now when I do this
 >>> x[1:+2]
['list2']

Does this puzzle anyone else

of course I am a total novice so I have no idea what I am doing here if 
anyone has any ideas please reply