This post explain the underlying architecture that supports Windows 7 libraries — “A Library in Windows 7 is stored as an XML definition file that has a file extension of “.library-ms.” The file name is the actual library’s name. For example, the Documents Library is represented by an XML file called Documents.library-ms. Library descriptions are saved on disk in the %appdata% Roaming\Microsoft\Windows\Libraries folder (also known as FOLDERID_Libraries).[…]”

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