Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/09/05/setting-a-flex-tool-tips-maximum-width/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.controls.ToolTip;
        ]]>
    </mx:Script>

    <mx:ApplicationControlBar dock="true">
        <mx:Label text="ToolTip.maxWidth:" />
        <mx:HSlider id="slider"
                minimum="50"
                maximum="300"
                value="{ToolTip.maxWidth}"
                liveDragging="true"
                snapInterval="5"
                tickInterval="10"
                dataTipPrecision="0"
                change="ToolTip.maxWidth = slider.value" />
        <mx:Label text="{slider.value}" />
    </mx:ApplicationControlBar>

    <mx:Button label="Roll over to see tool tip"
            toolTip="The quick brown fox jumped over the lazy dog." />

</mx:Application>

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