Edit in JSFiddle

;(function($) {
  // multiple plugins can go here
  (function(pluginName) {
    var defaults = {
      color: 'black',
      testFor: function(div) {
        return true;
      }
    };
    $.fn[pluginName] = function(options) {
      options = $.extend(true, {}, defaults, options);
            
      return this.each(function() {
        var elem = this,
          $elem = $(elem);
        // heres the guts of the plugin
          if (options.testFor(elem)) {
            $elem.css({
              borderWidth: 1,
              borderStyle: 'solid',
              borderColor: options.color
            });
          }
      });
    };
    $.fn[pluginName].defaults = defaults;
  })('borderize');
})(jQuery);


$('div').borderize();
$('span').borderize({color: 'red'});  

 <div>I'm a div</div>
 <span>I'm a span</span>