ByExtension Element (Document Icons)
Defines icons for documents according to their file name extensions.
This element is used in the DocIcon.xml file to drive mapping between file extensions and their corresponding document library icons.
If you want the document library feature to support a new file extension, add the extension to a ByExtension section and then restart the server.
See DocIcons Element (Document Icons) for an example that shows how to use the ByExtension element.