multiple(value, lower, upper) {
        if (value !== undefined) {
            value = VerbalExpression.sanitize(value);
            this.add(`(?:${value})`);
        }

        if (lower === undefined && upper === undefined) {
            this.add('*'); // Any number of times
        } else if (lower !== undefined && upper === undefined) {
            this.add(`{${lower},}`);
        } else if (lower !== undefined && upper !== undefined) {
            this.add(`{${lower},${upper}}`);
        }

        return this;
    }
Match the value zero or more times
@param {string} value value to find
@param {integer} [lower] minimum number of times the value should be repeated
@param {integer} [upper] maximum number of times the value should be repeated
@returns {VerbalExpression} recompiled instance of VerbalExpression
@memberof VerbalExpression