code: function validateAttributeUsage(className, attr, element, $log){
      var message, usage, url;
      var nodeName = element[0].nodeName.toLowerCase();
  
      switch (className.replace(SUFFIXES,"")) {
        case "flex":
          if ((nodeName == "md-button") || (nodeName == "fieldset")){
            // @see https://github.com/philipwalton/flexbugs#9-some-html-elements-cant-be-flex-containers
            // Use <div flex> wrapper inside (preferred) or outside
  
            usage = "<" + nodeName + " " + className + "></" + nodeName + ">";
            url = "https://github.com/philipwalton/flexbugs#9-some-html-elements-cant-be-flex-containers";
            message = "Markup '{0}' may not work as expected in IE Browsers. Consult '{1}' for details.";
  
            $log.warn($mdUtil.supplant(message, [usage, url]));
          }
      }
  
    }
docs: Centralize warnings for known flexbox issues (especially IE-related issues)