code: function rule(analyzer) {
  	analyzer.setMetric('notMinified');
  
  	/**
  	 * A simple CSS minification detector
  	 */
  	function isMinified(css) {
  		// analyze the first 1024 characters
  		css = css.trim().substring(0, 1024);
  
  		// there should be no newline in minified file
  		return /\n/.test(css) === false;
  	}
  
  	analyzer.on('css', function(css) {
  		analyzer.setMetric('notMinified', isMinified(css) ? 0 : 1);
  	});
  }
docs: Detect not minified CSS