The goal of this patch is to add a layer of indirection for className. The rationale is that the HTML DOM and the SVG DOM have different (and incompatible) interface definitions for className. Introducing a layer of indirection makes possible to provide uniform access to both HTML and SVG DOMs.

The attached patch affects any parts of jQuery which reference DOM's className. Currently, that means that only two parts of the jQuery core are affected:

1. jQuery.className.{add,remove,has}

2. The selector backend (the one which appears derived from Sizzle)

One of the most important effects of this patch is that it enables querying SVG elements by class name, e.g.:

   $("#my-svg-element .my-class") // this currently won't work
   // ...but it does work after applying the patch

Another important effect is that it makes possible to use addClass, hasClass, removeClass, and toggleClass.

A patch for this was originally proposed here:

http://groups.google.com/group/jquery-dev/browse_thread/thread/c2c56e4591f4f101

"Adding SVG class (className) support to jQuery"

If the developers seek to mitigate possible impacts on performance or browser compatibility, then the get/set accessors (see attached patch) could be rewritten like so:

  className: {
  
    get: function( elem ) {
      return elem.className;
    },
   
    set: function( elem, value ) {
      elem.className = value;
    },

    ...
  }

Although the above code causes jQuery to continue acting as it current does (and thus, will not support SVG className), it does provide a hook point for which plugins could override features. (Although I am not sure if this is a good idea since it seems hard to wrap/nest this such that one plugin simply extends another plugin.)

...then, conceivably, there could be a plugin which overrides the accessors to work like this (which is compatible with the SVG DOM):

jQuery.className.get = function( elem ) {
      var classNames = elem.getAttribute("class");
      classNames = classNames ? classNames : "";
      return classNames;
}

jQuery.className.set = function( elem, value ) {
    elem.setAttribute("class", value);
}

I have not done browser compatibility testing, nor I have I done performance testing. The only browser I have tested on is Firefox 3.0.8.