在textarea的光标处插入值

   var textArea=Ext.getCmp(textAreaId);
			var o = Ext.getDom(textAreaId); //The text box to be inserted   
			o.focus();			
      		var s = document.selection.createRange();//以先保存选区的方式用于在IE中实现插入   
      		var value = flag;   
		      if (document.selection) {//用于IE
		      	s.text = value; 
		      	s.moveEnd('character',value.length);  
                s.moveStart('character',value.length);  
		      }   
		      else {//用于FF   
		          o.value = o.value.substr(0, o.selectionStart) + value + o.value.substr(o.selectionEnd);   
		      }