The information required to tell the user there is a problem with their
input.
TODO: There a several places where {start,end} crop up. Perhaps we should
have a Cursor object.
function Hint(status, message, start, end, predictions) {
    this.status = status;
    this.message = message;

    if (typeof start === 'number') {
        this.start = start;
        this.end = end;
        this.predictions = predictions;
    }
    else {
        var arg = start;
        this.start = arg.start;
        this.end = arg.end;
        this.predictions = arg.predictions;
    }
}