docs: function validate( opts, options ) {
  	if ( !isObject( options ) ) {
  		return new TypeError( 'invalid argument. Options argument must be an object. Value: `' + options + '`.' );
  	}
  	if ( options.hasOwnProperty( 'radix' ) ) {
  		opts.radix = options.radix;
  		if ( !isInteger( opts.radix ) ) {
  			return new TypeError( 'invalid option. Radix must be an integer. Option: `' + opts.radix + '`.' );
  		}
  		if ( opts.radix < 2 || opts.radix > 36 ) {
  			return new RangeError( 'invalid option. Radix must be an integer on the interval [2,36]. Option: `' + opts.radix + '`.' );
  		}
  	}
  	return null;
  }