The source code

    /**
     * @class Ext.slider.Tip
     * @extends Ext.Tip
     * Simple plugin for using an Ext.Tip with a slider to show the slider value. Example usage:
    <pre>
    new Ext.Slider({
        width: 214,
        minValue: 0,
        maxValue: 100,
        plugins: new Ext.slider.Tip()
    });
    </pre>
     * Optionally provide your own tip text by overriding getText:
     <pre>
     new Ext.Slider({
         width: 214,
         minValue: 0,
         maxValue: 100,
         plugins: new Ext.slider.Tip({
             getText: function(thumb){
                 return String.format('<b>{0}% complete</b>', thumb.value);
             }
         })
     });
     </pre>
     */
    Ext.slider.Tip = Ext.extend(Ext.Tip, {
        minWidth: 10,
        offsets : [0, -10],

        init: function(slider) {
            slider.on({
                scope    : this,
                dragstart: this.onSlide,
                drag     : this.onSlide,
                dragend  : this.hide,
                destroy  : this.destroy
            });
        },

        /**
         * @private
         * Called whenever a dragstart or drag event is received on the associated Thumb.
         * Aligns the Tip with the Thumb's new position.
         * @param {Ext.slider.MultiSlider} slider The slider
         * @param {Ext.EventObject} e The Event object
         * @param {Ext.slider.Thumb} thumb The thumb that the Tip is attached to
         */
        onSlide : function(slider, e, thumb) {
            this.show();
            this.body.update(this.getText(thumb));
            this.doAutoWidth();
            this.el.alignTo(thumb.el, 'b-t?', this.offsets);
        },

        /**
         * Used to create the text that appears in the Tip's body. By default this just returns
         * the value of the Slider Thumb that the Tip is attached to. Override to customize.
         * @param {Ext.slider.Thumb} thumb The Thumb that the Tip is attached to
         * @return {String} The text to display in the tip
         */
        getText : function(thumb) {
            return String(thumb.value);
        }
    });

    //backwards compatibility - SliderTip used to be a ux before 3.2
    Ext.ux.SliderTip = Ext.slider.Tip;