If you haven't felt the need to animate the tabindex attribute, you're not trying hard enough

jquery.animate-attributes.js

/*!
 * jQuery element attributes CSS hooks & animation support
 *
 * Copyright © 2013 Lindsay Evans <http://linz.id.au/>
 * Licensed under the MIT <http://www.opensource.org/licenses/mit-license.php)> license.
 *
 * Why?
 * Why not
 *
 * Usage:
 * $('#foo').animate({'[border]': 10}, 'fast')
 *
 * TODO:
 * - Round integers? Things like min, max, value can be floats; others should be ints
 * - Deal with percentages (width etc.)
 * - Deal with colours (mmmm... bgcolor animation...)
 * - Any other silly deprecated attributes (hspace etc.)
 */

(function($){

  if(!$.cssHooks){
		throw('jQuery 1.4.3+ is needed for this plugin to work');
	}

	$(function(){

		// Loop over attribute names
		$.each([
			'tabindex', // oh god why
			'width','height', // <img>, <video> etc.
			'border', 'span', 'rowspan', 'colspan', // <table>, <th>, <td>, etc.
			'rows', 'cols', 'size', 'maxlength', 'value', 'min', 'max', 'step', // <input>, <textarea> etc.
			'high', 'low', 'optimum', // <meter>
			'start' // <ol>
		], function(k, v){

			// Property name is the attribute name wrapped in square brackets, CSS attribute selector style 
			var cssProperty = '[' + v + ']';

			// Attributes shouldn't have 'px'
			$.cssNumber[cssProperty] = true;

			// Getter & setter for the attribute
			$.cssHooks[cssProperty] = {
				get: function(elem, computed, extra){
					return elem[v];
				},
				set: function(elem, value){
					elem[v] = value;
				}
			};

			// Animation support for the attribute
			$.fx.step[cssProperty] = function(fx){
				$.cssHooks[cssProperty].set(fx.elem, fx.now);
			};
		});

	});

})(jQuery);