docs: function validate( opts, options ) {
  	if ( !isObject( options ) ) {
  		return new TypeError( 'invalid input argument. Options must be an object. Value: `' + options + '`.' );
  	}
  	if ( options.hasOwnProperty( 'allowHalfOpen' ) ) {
  		opts.allowHalfOpen = options.allowHalfOpen;
  		if ( !isBoolean( opts.allowHalfOpen ) ) {
  			return new TypeError( 'invalid option. Allow half open option must be a boolean primitive. Option: `' + opts.allowHalfOpen + '`.' );
  		}
  	}
  	if ( options.hasOwnProperty( 'highWaterMark' ) ) {
  		opts.highWaterMark = options.highWaterMark;
  		if ( !isNonNegative( opts.highWaterMark ) ) {
  			return new TypeError( 'invalid option. High watermark option must be a nonnegative number. Option: `' + opts.highWaterMark + '`.' );
  		}
  	}
  	return null;
  }