// NOTE: We only unpack `either` errors that occurred *at the same level* as this error, ie. where there's directly a case of `either(either(...), ...)`, without any kind of data nesting (like `arrayOf` or `hasShape`) inbetween. Nested-data failures should still be shown separately, as their resolution strategy is actually different; unlike same-level nested `either` errors, where the nesting is purely an implementation detail that allows composing sets of alternatives together.
thrownewError(`Must specify an array of alternatives`);
}elseif(alternatives.length<2){
// This doesn't interfere with conditionally-specified alternatives using ternary expressions, because in those cases there is still *some* item specified, it's just going to have a value of `undefined` (and will subsequently be filtered out)
thrownewError("Must specify at least two alternatives");
}elseif(arguments.length>1){
thrownewError(`Only one argument is accepted; maybe you forgot to wrap the different alternatives into an array?`);
// One of the alternatives *did* match, but it failed somewhere further down the tree, and we don't have any errors originating from *other* nested rules. Chances are that the user intended to match the failing branch, so we pretend that the other alternatives don't exist, and pass through the original error(s).