code: function Handler(level) {
  	level = level || Logger.NOTSET;
  
  	if (Logger.getLevelName(level) === '') {
  		throw new Error('Argument 1 of Handler.constructor has unsupported'
  			+ ' value \'' + level + '\'');
  	}
  
  	Filterer.call(this);
  
  	/**
  	 * @private
  	 * @type {number}
  	 */
  	this._level = level;
  
  	/**
  	 * @private
  	 * @type {Object}
  	 */
  	this._formatter = null;
  }
docs: An abstract handler.
  
  @constructor Handler
  @extends Filterer
  @param {number} [level=NOTSET]