Directions on Christmas (to all the PC people out there: holiday) lights:
For indoor or outdoor use only.
The 'only' portion of that phrase was probably either a typo. or a leftover from the old days when there were indeed separate indoor and outdoor strings. The main difference between indoor and outdoor light strings was whether or not the sockets were weatherproof.
Once upon a time, the now-non-existent C6
series and the C7 (candelabra base) strings were strictly indoor light sets and the C9
(intermediate base) strings were outdoor lights with weatherproof sockets.
Back to the topic at hand, some directions nowadays are absolutely ridiculous. My personal favorite instruction glitches are ones that were translated into English from another language.
"TransEastern! You'll feel like you've never left the ground because we treat you like dirt!" SNL Parady ad circa 1981