Panels (20A, 20B) are attached to extrusions (66A, 66B) by fasteners 90. Clips (70) are attached to a structure (50) by fasteners (35). The extrusions and the clips engage in a manner which allows the panels to move in any direction, as needed, without the panel detaching from the structure and falling. The extrusions also provide for the use of optional reveal strips (87). An extrusion has a restraining area (86), a reveal strip stop area (58), and a T-slot (65). A clip has a T-channel (74), a tensioning stop arm (69), and a secondary reinforcing arm (80). The panels can be installed in rows, in columns, or diagonally, as desired.