> -1:1 means the last character.

Earlier you said:
" -10:3 -- 3 characters starting at the 10th from last."
leaving it an open question whether the "10" is zero- or one-based
(confusion enough) so you're saying that it's one-based.  Ok. then
(inevitably)  0:1 is going to be supported and will mean the first
character.

I just think this is going to take too much 'splaining.