`contains` tests whether the set `VALUES` contains the string `KEY`. If so, `contains` exits with status 0; if not, it exits with status 1.
The following options are available:
-`-i` or `--index` print the word index
Note that, like GNU tools and most of fish's builtins, `contains` interprets all arguments starting with a `-` as options to contains, until it reaches an argument that is `--` (two dashes). See the examples below.