You don't find the quote from perltrap interesting? Not even the fact that they have effectively the same assignment (from a list to a scalar) and claim that the result will be the length of the list? I.E. that note in perltrap is wrong, at least for those versions of perl that I have access to.
I do find that interesting because that's the first documentation I found when looking for what the documented behaviour would be. My method was look to grep perltoc for slice and context and then look in the pages it pointed at.
If this isn't going to be documented under the docs for slice (IMHO the correct place), then the other places need to be correct. Or we'll have people reporting bugs because they can't find the correct documentation.