Used to create a separator between menu items..

    <menu label="File">
    <menupopup>    
        <menuitem label="New" onClick="alert(self.label)"/>        
        <menuitem label="Open" onClick="alert(self.label)"/>        
        <menuitem label="Save" onClick="alert(self.label)"/>        
        <menuseparator/>        
        <menuitem label="Exit" onClick="alert(self.label)"/>        
    </menupopup>    
</menu>