Difference between use="" and apply=""

<window use="myWinClass">
</window>

<rows id="tableGridRows">
			<row self="@{each=entry}">
				<intbox value="@{entry.mfifir}" cols="2" maxlength="2" format="##" tooltip="help"/>
				<label value="@{entry.mfifirkbez}" tooltip="help"/>
                                ...
				<image id="trash" src="images/trash empty_24.png" hover="images/trash full_24.png"/>
			</row>
		</rows>	

in my Javaclass (could be ext. Window or Composer)
public void onClick$trash(Event event) { // handels onClick from trashicon

button.addForward("onClick", win, "onClickTrash");

public void onClickTrash(Event event) { // handels onClick from trashbutton

public void render(Listitem item, Object obj)
{
   // Create your row
   // ...

   // Now it's time to create the button:
   Button btn = new Button();
   // Configure your button with your label, etc...
   // Now that your button is ready, add this (I save the data as button attribute):
   btn.addAttribute("CUSTOMERDATA", obj);
   ComponentsCtrl.applyForward(btn, "onClick=onButtonHasClickedInList");
}

// ...
// Your composer code
// ...

// Here is the method that will handle the clicks on the list buttons:

public void onButtonHasClickedInList(Event evt)
{
   // The event is a ForwardEvent...
   ForwardEvent fe = (ForwardEvent) evt;
   // Getting the original Event
   Event evt = fe.getOrigin();

   // Getting the component that triggered the original event (i.e. the button)
   Button btn = (Button) evt.getTarget();

   // Getting the Customer Data (it can be any type. for the example, I'll use Object)..
   // Each button will have it's own customer data instance
   Object obj = btn.getAttribute("CUSTOMERDATA");
   
   // Do what you want with the customer data

}

<zk>
<zscript>
class comp extends org.zkoss.zk.ui.util.GenericForwardComposer
{
   public void onButtonClicked(Event evt)
   {
       ForwardEvent fe = (ForwardEvent) evt;
       Event e = fe.getOrigin();
       Button btn = (Button) e.getTarget();
       alert ("LIST ITEM DATA : " + btn.getAttribute("DATA"));

   }
}
</zscript>
<window title="Listbox" border="normal" use="comp">
	<vbox>
		<listbox width="250px" id="myList">
			<listhead sizable="true">
				<listheader label="Name" sort="auto"/>
				<listheader label="Action"/>
			</listhead>
		</listbox>
               <zscript>
<![CDATA[

    List data = new ArrayList();
    for (int i = 0; i < 2; )
       data.add("ITEM : " + ++i);

myList.setModel(new ListModelList(data));

myList.setItemRenderer(
new ListitemRenderer()
{
   void render(Listitem item,
               java.lang.Object data)
   {
      Listcell cell = new Listcell();

      Label lbl = new Label(data.toString());
      lbl.setParent(cell);
      cell.setParent(item);

      Listcell cell = new Listcell();
      Button btn = new Button();
      btn.setLabel("Click me");
      btn.setParent(cell);
      btn.setAttribute("DATA", data);
      cell.setParent(item);
      ComponentsCtrl.applyForward(btn, "onClick=onButtonClicked");
   }
}
);


]]>
</zscript>
	</vbox>
</window>
</zk>