Objects on a page are arranged in layers along the z (or back to front) index, making it possible for one object to cover another one.
Objects closer to the viewer are closer to the front and objects closer to the applet page are closer to the back.
The Arrange tools on the Edit drop-down menu move objects forward or backward in the z-order.
Arrange > Bring to Front - Move an object to the front of the page,which places it on top of any other objects on the page
Arrange > Bring Forward - Move an object one layer closer to the front of the page.
Arrange > Send Backward - Move an object one layer closer to the back of the page.
Arrange > Send to Back - Move an object to the back of the page, which places it behind or under any other objects on the page.
Note : The z-order of objects on a page can also be controlled using the Arrange tools on the Common Bar, or by dragging objects to a different place in the Objects list, which is on the Objects tab of the Project Panel.