[This is preliminary documentation and subject to change.]
An extension Snap-In provides functionality only when invoked by a primary Snap-In. An extension Snap-In can extend given node types only. It declares itself as being a subordinate to nodes of certain types, and then for each occurrence of those node types, the console automatically adds the related Snap-In extensions.
For example, an extension snap-in might be a "Log Pretty Print" Snap-In, providing users several ways to print out log files (such as the Windows NT Event Log). With this snap-in installed, every log object in the namespace would be extended with the "Pretty Print" context menu item.
Extension Snap-Ins can provide a variety of functionality. Some can actually extend the console namespace (for example, a Snap-In that provides system information about computers would add that information to the namespace under each computer in the namespace), while others simply extend context menus or specific wizards. For more information, see the section, Extension Features For Snap-Ins, later in this document.