code: function validate( opts, options ) {
  	if ( !isObject( options ) ) {
  		return new TypeError( 'invalid input argument. Options argument must be an object. Option: `' + options + '`.' );
  	}
  	if ( options.hasOwnProperty( 'flavor' ) ) {
  		opts.flavor = options.flavor;
  		if ( !isString( opts.flavor ) ) {
  			return new TypeError( 'invalid option. Markdown flavor option must be a string primitive. Option: `' + opts.flavor + '`.' );
  		}
  	}
  	return null;
  }
docs: VALIDATE // 
  FUNCTION: validate( opts, options )
  Validates function options.
  
  @param {Object} opts - destination object
  @param {Object} options - options to validate
  @param {String} [options.flavor] - Markdown flavor
  @returns {Error|Null} error or null