The source code

    /*!
     * Ext JS Library 3.2.1
     * Copyright(c) 2006-2010 Ext JS, Inc.
     * licensing@extjs.com
     * http://www.extjs.com/license
     */
    /**
     * @class Ext.Element
     */
    /**
     * Visibility mode constant for use with {@link #setVisibilityMode}. Use visibility to hide element
     * @static
     * @type Number
     */
    Ext.Element.VISIBILITY = 1;
    /**
     * Visibility mode constant for use with {@link #setVisibilityMode}. Use display to hide element
     * @static
     * @type Number
     */
    Ext.Element.DISPLAY = 2;

    Ext.Element.addMethods(function(){
        var VISIBILITY = "visibility",
            DISPLAY = "display",
            HIDDEN = "hidden",
            OFFSETS = "offsets",
            NONE = "none",
            ORIGINALDISPLAY = 'originalDisplay',
            VISMODE = 'visibilityMode',
            ELDISPLAY = Ext.Element.DISPLAY,
            data = Ext.Element.data,
            getDisplay = function(dom){
                var d = data(dom, ORIGINALDISPLAY);
                if(d === undefined){
                    data(dom, ORIGINALDISPLAY, d = '');
                }
                return d;
            },
            getVisMode = function(dom){
                var m = data(dom, VISMODE);
                if(m === undefined){
                    data(dom, VISMODE, m = 1);
                }
                return m;
            };

        return {
            /**
             * The element's default display mode  (defaults to "")
             * @type String
             */
            originalDisplay : "",
            visibilityMode : 1,

            /**
             * Sets the element's visibility mode. When setVisible() is called it
             * will use this to determine whether to set the visibility or the display property.
             * @param {Number} visMode Ext.Element.VISIBILITY or Ext.Element.DISPLAY
             * @return {Ext.Element} this
             */
            setVisibilityMode : function(visMode){
                data(this.dom, VISMODE, visMode);
                return this;
            },

            /**
             * Perform custom animation on this element.
             *
             * Animation Properties
             *
             * The Animation Control Object enables gradual transitions for any member of an
             * element's style object that takes a numeric value including but not limited to
             * these properties:
             * bottom, top, left, right
             * height, width
             * margin, padding
             * borderWidth
             * opacity
             * fontSize
             * lineHeight
             *
             *
             *
             * Animation Property Attributes
             *
             * Each Animation Property is a config object with optional properties:
             *
             * by*  : relative change - start at current value, change by this value
             * from : ignore current value, start from this value
             * to*  : start at current value, go to this value
             * unit : any allowable unit specification
             * * do not specify both to and by for an animation property
             *
             *
             * Animation Types
             *
             * The supported animation types:
             * 'run' : Default
             *
    var el = Ext.get('complexEl');
    el.animate(
        // animation control object
        {
            borderWidth: {to: 3, from: 0},
            opacity: {to: .3, from: 1},
            height: {to: 50, from: el.getHeight()},
            width: {to: 300, from: el.getWidth()},
            top  : {by: - 100, unit: 'px'},
        },
        0.35,      // animation duration
        null,      // callback
        'easeOut', // easing method
        'run'      // animation type ('run','color','motion','scroll')
    );
             *
             *
             * 'color'
             * Animates transition of background, text, or border colors.
             *
    el.animate(
        // animation control object
        {
            color: { to: '#06e' },
            backgroundColor: { to: '#e06' }
        },
        0.35,      // animation duration
        null,      // callback
        'easeOut', // easing method
        'color'    // animation type ('run','color','motion','scroll')
    );
             *
             *
             *
             * 'motion'
             * Animates the motion of an element to/from specific points using optional bezier
             * way points during transit.
             *
    el.animate(
        // animation control object
        {
            borderWidth: {to: 3, from: 0},
            opacity: {to: .3, from: 1},
            height: {to: 50, from: el.getHeight()},
            width: {to: 300, from: el.getWidth()},
            top  : {by: - 100, unit: 'px'},
            points: {
                to: [50, 100],  // go to this point
                control: [      // optional bezier way points
                    [ 600, 800],
                    [-100, 200]
                ]
            }
        },
        3000,      // animation duration (milliseconds!)
        null,      // callback
        'easeOut', // easing method
        'motion'   // animation type ('run','color','motion','scroll')
    );
             *
             *
             * 'scroll'
             * Animate horizontal or vertical scrolling of an overflowing page element.
             *
    el.animate(
        // animation control object
        {
            scroll: {to: [400, 300]}
        },
        0.35,      // animation duration
        null,      // callback
        'easeOut', // easing method
        'scroll'   // animation type ('run','color','motion','scroll')
    );
             *
             *
             *
             *
             *
             *
             * @param {Object} args The animation control args
             * @param {Float} duration (optional) How long the animation lasts in seconds (defaults to .35)
             * @param {Function} onComplete (optional) Function to call when animation completes
             * @param {String} easing (optional) {@link Ext.Fx#easing} method to use (defaults to 'easeOut')
             * @param {String} animType (optional) 'run' is the default. Can also be 'color',
             * 'motion', or 'scroll'
             * @return {Ext.Element} this
             */
            animate : function(args, duration, onComplete, easing, animType){
                this.anim(args, {duration: duration, callback: onComplete, easing: easing}, animType);
                return this;
            },

            /*
             * @private Internal animation call
             */
            anim : function(args, opt, animType, defaultDur, defaultEase, cb){
                animType = animType || 'run';
                opt = opt || {};
                var me = this,
                    anim = Ext.lib.Anim[animType](
                        me.dom,
                        args,
                        (opt.duration || defaultDur) || .35,
                        (opt.easing || defaultEase) || 'easeOut',
                        function(){
                            if(cb) cb.call(me);
                            if(opt.callback) opt.callback.call(opt.scope || me, me, opt);
                        },
                        me
                    );
                opt.anim = anim;
                return anim;
            },

            // private legacy anim prep
            preanim : function(a, i){
                return !a[i] ? false : (typeof a[i] == 'object' ? a[i]: {duration: a[i+1], callback: a[i+2], easing: a[i+3]});
            },

            /**
             * Checks whether the element is currently visible using both visibility and display properties.
             * @return {Boolean} True if the element is currently visible, else false
             */
            isVisible : function() {
                return !this.isStyle(VISIBILITY, HIDDEN) && !this.isStyle(DISPLAY, NONE);
            },

            /**
             * Sets the visibility of the element (see details). If the visibilityMode is set to Element.DISPLAY, it will use
             * the display property to hide the element, otherwise it uses visibility. The default is to hide and show using the visibility property.
             * @param {Boolean} visible Whether the element is visible
             * @param {Boolean/Object} animate (optional) True for the default animation, or a standard Element animation config object
             * @return {Ext.Element} this
             */
             setVisible : function(visible, animate){
                var me = this, isDisplay, isVisible, isOffsets,
                    dom = me.dom;

                // hideMode string override
                if (typeof animate == 'string'){
                    isDisplay = animate == DISPLAY;
                    isVisible = animate == VISIBILITY;
                    isOffsets = animate == OFFSETS;
                    animate = false;
                } else {
                    isDisplay = getVisMode(this.dom) == ELDISPLAY;
                    isVisible = !isDisplay;
                }

                if (!animate || !me.anim) {
                    if (isDisplay){
                        me.setDisplayed(visible);
                    } else if (isOffsets){
                        if (!visible){
                            me.hideModeStyles = {
                                position: me.getStyle('position'),
                                top: me.getStyle('top'),
                                left: me.getStyle('left')
                            };

                            me.applyStyles({position: 'absolute', top: '-10000px', left: '-10000px'});
                        } else {
                            me.applyStyles(me.hideModeStyles || {position: '', top: '', left: ''});
                        }
                    }else{
                        me.fixDisplay();
                        dom.style.visibility = visible ? "visible" : HIDDEN;
                    }
                }else{
                    // closure for composites
                    if (visible){
                        me.setOpacity(.01);
                        me.setVisible(true);
                    }
                    me.anim({opacity: { to: (visible?1:0) }},
                            me.preanim(arguments, 1),
                            null,
                            .35,
                            'easeIn',
                            function(){
                                 if(!visible){
                                     dom.style[isDisplay ? DISPLAY : VISIBILITY] = (isDisplay) ? NONE : HIDDEN;
                                     Ext.fly(dom).setOpacity(1);
                                 }
                            });
                }
                return me;
            },

            /**
             * Toggles the element's visibility or display, depending on visibility mode.
             * @param {Boolean/Object} animate (optional) True for the default animation, or a standard Element animation config object
             * @return {Ext.Element} this
             */
            toggle : function(animate){
                var me = this;
                me.setVisible(!me.isVisible(), me.preanim(arguments, 0));
                return me;
            },

            /**
             * Sets the CSS display property. Uses originalDisplay if the specified value is a boolean true.
             * @param {Mixed} value Boolean value to display the element using its default display, or a string to set the display directly.
             * @return {Ext.Element} this
             */
            setDisplayed : function(value) {
                if(typeof value == "boolean"){
                   value = value ? getDisplay(this.dom) : NONE;
                }
                this.setStyle(DISPLAY, value);
                return this;
            },

            // private
            fixDisplay : function(){
                var me = this;
                if(me.isStyle(DISPLAY, NONE)){
                    me.setStyle(VISIBILITY, HIDDEN);
                    me.setStyle(DISPLAY, getDisplay(this.dom)); // first try reverting to default
                    if(me.isStyle(DISPLAY, NONE)){ // if that fails, default to block
                        me.setStyle(DISPLAY, "block");
                    }
                }
            },

            /**
             * Hide this element - Uses display mode to determine whether to use "display" or "visibility". See {@link #setVisible}.
             * @param {Boolean/Object} animate (optional) true for the default animation or a standard Element animation config object
             * @return {Ext.Element} this
             */
            hide : function(animate){
                // hideMode override
                if (typeof animate == 'string'){
                    this.setVisible(false, animate);
                    return this;
                }
                this.setVisible(false, this.preanim(arguments, 0));
                return this;
            },

            /**
            * Show this element - Uses display mode to determine whether to use "display" or "visibility". See {@link #setVisible}.
            * @param {Boolean/Object} animate (optional) true for the default animation or a standard Element animation config object
             * @return {Ext.Element} this
             */
            show : function(animate){
                // hideMode override
                if (typeof animate == 'string'){
                    this.setVisible(true, animate);
                    return this;
                }
                this.setVisible(true, this.preanim(arguments, 0));
                return this;
            }
        };
    }());