<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/04/25/setting-text-selection-on-a-textarea-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            import mx.core.IUITextField;
            import mx.events.SliderEvent;
            import mx.controls.sliderClasses.Slider;

            private function slider_change(evt:SliderEvent):void {
                textArea.selectionBeginIndex = beginSlider.value;
                textArea.selectionEndIndex = endSlider.value;
                
                textArea.validateNow();
                beginLabel.text = textArea.selectionBeginIndex.toString();
                endLabel.text = textArea.selectionEndIndex.toString();
            }

            private function init():void {
                var tf:IUITextField = textArea.mx_internal::getTextField();
                tf.alwaysShowSelection = true;
                textArea.verticalScrollPosition = 0;
            }
        ]]>
    </mx:Script>

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

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="selectionBeginIndex:"
                    direction="horizontal">
                <mx:HSlider id="beginSlider"
                        minimum="0"
                        maximum="{textArea.htmlText.length}"
                        value="0"
                        liveDragging="true"
                        change="slider_change(event);" />
                <mx:Label id="beginLabel" />
            </mx:FormItem>
            <mx:FormItem label="selectionEndIndex:"
                    direction="horizontal">
                <mx:HSlider id="endSlider"
                        minimum="0"
                        maximum="{textArea.htmlText.length}"
                        value="0"
                        snapInterval="1"
                        liveDragging="true"
                        change="slider_change(event);" />
                <mx:Label id="endLabel" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:TextArea id="textArea"
            htmlText="{lorem}"
            textAlign="justify"
            condenseWhite="true"
            width="100%"
            height="100%"
            creationComplete="init();" />

</mx:Application>