NetFirewallRule.cmdletDefinition.cdxml

PowerShell cmdlet definition XML

A .cdxml file contains a cmdlet definition in XML for PowerShell. The file maps a WMI or CIM class to PowerShell cmdlets. PowerShell reads the file and creates the cmdlets without compiled code. Many Windows management modules use this technique. The name of the format is cmdlet definition XML, or CDXML.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.