This is an example of object manipulations using Visual LISP. The command function Dax included in this tip detaches all external references in a drawing that are not on locked layers. This tip is an excellent demonstration of how to loop through a block table using object references in Visual LISP. Each object in the block table is first checked to see if it is an external reference. When an external reference block is found, all instances of the block in the drawing are collected into a selection set. That selection set then is processed in a loop in which items on unlocked layers are detached (resulting in a normal internal block reference). This example is wonderful for advanced programmers who are looking to see how selection sets, lists, and Visual LISP object references can work together elegantly.