IndexOf takes the length of a sequence and an ElementPredicate that can determine if the element at a given index is equal to what we're looking for.

Int returns the location of a target string within a []int or -1 if it is not found.

String returns the location of a target string within a []string or -1 if it is not found.

TrimmedString returns the location of a target string within a []string or -1 if it is not found.

NotFound indicates no element matching a predicate was found.

ElementPredicate is a function that applies some predicate to an element of a slice at a given index.