The source code

    /**
     * @class Ext.Tip
     * @extends Ext.Panel
     * @xtype tip
     * This is the base class for {@link Ext.QuickTip} and {@link Ext.Tooltip} that provides the basic layout and
     * positioning that all tip-based classes require. This class can be used directly for simple, statically-positioned
     * tips that are displayed programmatically, or it can be extended to provide custom tip implementations.
     * @constructor
     * Create a new Tip
     * @param {Object} config The configuration options
     */
    Ext.Tip = Ext.extend(Ext.Panel, {
        /**
         * @cfg {Boolean} closable True to render a close tool button into the tooltip header (defaults to false).
         */
        /**
         * @cfg {Number} width
         * Width in pixels of the tip (defaults to auto).  Width will be ignored if it exceeds the bounds of
         * {@link #minWidth} or {@link #maxWidth}.  The maximum supported value is 500.
         */
        /**
         * @cfg {Number} minWidth The minimum width of the tip in pixels (defaults to 40).
         */
        minWidth : 40,
        /**
         * @cfg {Number} maxWidth The maximum width of the tip in pixels (defaults to 300).  The maximum supported value is 500.
         */
        maxWidth : 300,
        /**
         * @cfg {Boolean/String} shadow True or "sides" for the default effect, "frame" for 4-way shadow, and "drop"
         * for bottom-right shadow (defaults to "sides").
         */
        shadow : "sides",
        /**
         * @cfg {String} defaultAlign <b>Experimental</b>. The default {@link Ext.Element#alignTo} anchor position value
         * for this tip relative to its element of origin (defaults to "tl-bl?").
         */
        defaultAlign : "tl-bl?",
        autoRender: true,
        quickShowInterval : 250,

        // private panel overrides
        frame:true,
        hidden:true,
        baseCls: 'x-tip',
        floating:{shadow:true,shim:true,useDisplay:true,constrain:false},
        autoHeight:true,

        closeAction: 'hide',

        // private
        initComponent : function(){
            Ext.Tip.superclass.initComponent.call(this);
            if(this.closable && !this.title){
                this.elements += ',header';
            }
        },

        // private
        afterRender : function(){
            Ext.Tip.superclass.afterRender.call(this);
            if(this.closable){
                this.addTool({
                    id: 'close',
                    handler: this[this.closeAction],
                    scope: this
                });
            }
        },

        /**
         * Shows this tip at the specified XY position.  Example usage:
         * <pre><code>
    // Show the tip at x:50 and y:100
    tip.showAt([50,100]);
    </code></pre>
         * @param {Array} xy An array containing the x and y coordinates
         */
        showAt : function(xy){
            Ext.Tip.superclass.show.call(this);
            if(this.measureWidth !== false && (!this.initialConfig || typeof this.initialConfig.width != 'number')){
                this.doAutoWidth();
            }
            if(this.constrainPosition){
                xy = this.el.adjustForConstraints(xy);
            }
            this.setPagePosition(xy[0], xy[1]);
        },

        // protected
        doAutoWidth : function(adjust){
            adjust = adjust || 0;
            var bw = this.body.getTextWidth();
            if(this.title){
                bw = Math.max(bw, this.header.child('span').getTextWidth(this.title));
            }
            bw += this.getFrameWidth() + (this.closable ? 20 : 0) + this.body.getPadding("lr") + adjust;
            this.setWidth(bw.constrain(this.minWidth, this.maxWidth));

            // IE7 repaint bug on initial show
            if(Ext.isIE7 && !this.repainted){
                this.el.repaint();
                this.repainted = true;
            }
        },

        /**
         * <b>Experimental</b>. Shows this tip at a position relative to another element using a standard {@link Ext.Element#alignTo}
         * anchor position value.  Example usage:
         * <pre><code>
    // Show the tip at the default position ('tl-br?')
    tip.showBy('my-el');

    // Show the tip's top-left corner anchored to the element's top-right corner
    tip.showBy('my-el', 'tl-tr');
    </code></pre>
         * @param {Mixed} el An HTMLElement, Ext.Element or string id of the target element to align to
         * @param {String} position (optional) A valid {@link Ext.Element#alignTo} anchor position (defaults to 'tl-br?' or
         * {@link #defaultAlign} if specified).
         */
        showBy : function(el, pos){
            if(!this.rendered){
                this.render(Ext.getBody());
            }
            this.showAt(this.el.getAlignToXY(el, pos || this.defaultAlign));
        },

        initDraggable : function(){
            this.dd = new Ext.Tip.DD(this, typeof this.draggable == 'boolean' ? null : this.draggable);
            this.header.addClass('x-tip-draggable');
        }
    });

    Ext.reg('tip', Ext.Tip);

    // private - custom Tip DD implementation
    Ext.Tip.DD = function(tip, config){
        Ext.apply(this, config);
        this.tip = tip;
        Ext.Tip.DD.superclass.constructor.call(this, tip.el.id, 'WindowDD-'+tip.id);
        this.setHandleElId(tip.header.id);
        this.scroll = false;
    };

    Ext.extend(Ext.Tip.DD, Ext.dd.DD, {
        moveOnly:true,
        scroll:false,
        headerOffsets:[100, 25],
        startDrag : function(){
            this.tip.el.disableShadow();
        },
        endDrag : function(e){
            this.tip.el.enableShadow(true);
        }
    });