<?xml version="1.0" encoding="utf-8"?>

<!-- tooltips/BoundToolTipText.mxml -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

  <mx:TextInput id="txtTo" width="300"/>

  <mx:Button label="Send" toolTip="Send e-mail to {txtTo.text}"/>

</mx:Application>

<?xml version="1.0" encoding="utf-8"?>

<!-- tooltips/DynamicToolTipText.mxml -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" initialize="initApp()">

  <mx:Script>

    <![CDATA[
     import mx.managers.ToolTipManager;
     import mx.controls.ToolTip;
     import mx.events.ToolTipEvent;

     public function initApp():void {

        b1.addEventListener(ToolTipEvent.TOOL_TIP_SHOW, myToolTipChanger)
     }

     public function myToolTipChanger(event:ToolTipEvent):void

     {
        ToolTipManager.currentToolTip.text = "Click the button, " +
            Application.application.parameters.myName;
     }

    ]]>
  </mx:Script>

    <mx:Button id="b1" label="Click Me" toolTip="Click the button."/>

</mx:Application>