    "The `Boolean` value of the given string representation of a
     boolean value, or `null` if the string does not represent a
     boolean value.

     Recognized values are `\"true\"`, `\"false\"`."
    tagged("Basic types")
    shared Boolean? parseBoolean(String string) {
        switch (string)
        case ("true") { return true; }
        case ("false") { return false; }
        else { return null; }
    }