value: p.replace(/\$\$/g, '$'), arg: null};
                }

                // Otherwise, return the substitution value.
                return {value: varArgs[p[1]], arg: p};
            });

            return pieces;
        }

        /**
   * As above, but also makes sure that the value is a boolean.
   * @param {string} id The key that identifies the desired boolean.
   * @return {boolean} The corresponding boolean value.
   */
        getBoolean(id) {
            const value = this.getValue(id);
 