In Leopard, the dock is entirely different from any previous version of OS X. Its first real major revision of the Dock since the inception of OS X. It now has a new glass surface that the icons sit on. Windows reflect off the glass when placed under it. The Dock also has a new feature called Stacks. Stacks is an easy way to have easy access to the entire contents of a folder. It also is the new default location for all downloads from Safari and Mail. You can create your own stacks by selecting a group of icons and then dragging them to the dock, it will automatically create a stack for you. When clicked on, they will spring out in either a single row, or a grid if there are too many for a single row.
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