<?xml version="1.0" encoding="utf-8"?>
  <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">
      
      <mx:Script>
          <![CDATA[
  // Define private variable.
      private var _maxFontSize:Number = 15;
  
      [Bindable(event="maxFontSizeChanged")]
      // Define public getter method.
      public function get maxFontSize():Number {
          return _maxFontSize;
      }
  
      // Define public setter method.
      public function set maxFontSize(value:Number):void {
          if (value <= 30) {
              _maxFontSize = value;
          } else _maxFontSize = 30;
  
          // Create event object. 
         var eventObj:Event = new Event("maxFontSizeChanged");
         dispatchEvent(eventObj);
  
      }
              
              
          ]]>
      </mx:Script>
      <mx:TextInput id="myTi" change="maxFontSize=Number(myTi.text)"/>
      <mx:TextInput id="myTi2" text="{maxFontSize}"/>
      
  </mx:Application>