function accumulator( x ) {
		if ( arguments.length === 0 ) {
			return ( max === void 0 ) ? null : max;
		}
		if (
			max === void 0 ||
			x > max ||
			isnan( x ) ||
			( x === max && isPositiveZero( x ) )
		) {
			max = x;
		}
		return max;
	}
If provided a value, the accumulator function returns an updated maximum value. If not provided a value, the accumulator function returns the current max.

@private
@param {number} [x] - new value
@returns {(number|null)} max value or null