<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/11/21/creating-a-custom-scroll-tip-function-on-a-flex-textarea-control/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            private function textArea_scrollTipFunc(direction:String, position:Number):String {
                var str:String;
                switch (direction) {
                    case "horizontal":
                        str = position + "/" + textArea.maxHorizontalScrollPosition;
                        break;
                    case "vertical":
                        str = position + "/" + textArea.maxVerticalScrollPosition;
                        break;
                }
                return str;
            }
        ]]>
    </mx:Script>

    <mx:String id="lorem" source="lorem.txt" />

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="showScrollTips:">
                <mx:CheckBox id="checkBox" selected="true" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:TextArea id="textArea"
            text="{lorem}" wordWrap="false"
            showScrollTips="{checkBox.selected}"
            scrollTipFunction="textArea_scrollTipFunc"
            width="100%"
            height="100%" />

</mx:Application>