<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
	<mx:Script>
		<![CDATA[
		import mx.utils.StringUtil;
		[Bindable]
		private var longString:String = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
		private var maxStringLength:int = 50;
		private function truncatedString(source:String):String {
			var shortString:String = StringUtil.trim(source);
			shortString = shortString.substr(0, maxStringLength);
			if (source.length != 0 && source.length > maxStringLength) {
				shortString += "...";
			}
			return shortString;
		}
		]]>
	</mx:Script>
	<mx:Panel layout="absolute" left="10" right="10" bottom="10" top="10">
		<mx:TextArea x="10" y="10" maxWidth="200" maxHeight="50" text="{truncatedString(longString)}" id="lblLongText" height="65" wordWrap="true"/>
	</mx:Panel>

</mx:Application>

<mx:Label id="_alabel" text="hello" toolTip="{_alabel.text}" />

secondly, you could subclass label and override the setter for the text property and assigning the text being set to the tooltip. i haven’t tried this, so this code is off the top of my head:

public class TippedLabel extends Label {

  override public function set text(o:String) : void {
    super.text = o;
    super.toolTip = o;
  }

}

Hope that helps.

Cheers,
Chris

Here what you can find in Label.as :

// Plain text gets truncated with a "...".
// HTML text simply gets clipped, because it is difficult
// to skip over the markup and truncate only the non-markup.
// But both plain text and HTML text gets an automatic tooltip
// if the full text isn't visible.