You also need to set tabStops.  For example, paraElement.tabStops = "36 72".

By default in current player a tab without a tabStop results in a new line.  Current thinking is that's a bug and player will add default tab stops.

Richard

The problem here is that you have more tabs than tabstops, so the extra tabs take up the remaining space on the line.You can either just use one tab, with one tabstop set where you want it, or use multiple tabs with multiple tabstops.

I also notice you're using an older build. You can get a newer (improved!) build posted as part of the Flex Gumbo SDK.

Here's some newer code that would work:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="paragraphFormat()">
    <mx:Script>
        <![CDATA[
            import flashx.textLayout.container.ContainerController;
            import flashx.textLayout.elements.SpanElement;
            import flashx.textLayout.elements.ParagraphElement;
            import flash.text.engine.TabAlignment;
            import flashx.textLayout.formats.TabStopFormat;
            import flashx.textLayout.formats.TextLayoutFormat;
            import flashx.textLayout.elements.TextFlow;
          
            private var textContainer:Sprite = null;
            public function paragraphFormat():void
            {
                textContainer = new Sprite();
                var textFlow:TextFlow = new TextFlow();
                var paraFormat:TextLayoutFormat = new TextLayoutFormat();
                paraFormat.paragraphStartIndent = 15;
                paraFormat.paragraphSpaceBefore = 15;
                paraFormat.paragraphEndIndent = 15;
                paraFormat.paragraphSpaceAfter = 15;
                paraFormat.textIndent = 8;
              
                var tabStop1:TabStopFormat = new TabStopFormat();
                tabStop1.alignment = TabAlignment.CENTER;
                tabStop1.position = 100;
                var tabStop2:TabStopFormat = new TabStopFormat();
                tabStop2.alignment = TabAlignment.CENTER;
                tabStop2.position = 200;
                 var tabStop3:TabStopFormat = new TabStopFormat();
                tabStop3.alignment = TabAlignment.CENTER;
                tabStop3.position = 300;
                paraFormat.tabStops = [tabStop1, tabStop2, tabStop3];              
                textFlow.hostFormat = paraFormat;
              
              
                var p:ParagraphElement = new ParagraphElement();
                var span:SpanElement = new SpanElement();
                span.text = "123\t\t\t456.";
                //trace("text : "+ span.text);
                span.fontSize = 32;
                p.addChild(span);
                textFlow.addChild(p);
              
                textFlow.flowComposer.addController(new ContainerController(textContainer,400,500));
                textFlow.flowComposer.updateAllControllers();
                canvas.rawChildren.addChild(textContainer);
            }

        ]]>
    </mx:Script>
    <mx:Canvas id="canvas" width="720" height="540"  backgroundColor="#ECE9D8" verticalScrollPolicy="auto" borderColor="#000000"  />
</mx:Application>

Well, you could just add a lot of tab stops; doesn't hurt to have too many. Or if for some reason you don't want to do that, you could programmatically count the tabs and add the correct number.  I'm afraid I don't have a better solution.

- robin