indexOf

Returns the index of the first occurrence of substr in s. Returns -1 if not found.

Example:

    assert (Strings.indexOf ("hello world", "world") == 6);
    assert (Strings.indexOf ("hello", "xyz") == -1);

Parameters:

s	the string to search in.
substr	the substring to find.

Returns:

index of first occurrence, or -1 if not found.