A virtual file has both of the following elements:
A behavior definition, which is also known as a Transformation Template (see Transformation Templates) and provides instructions to the virtual file system so it can render virtual data in an appropriate manner
Virtual contents, which is the content generated at the time the file is read
The transformation template (behavior definition) for a virtual file is created by opening the file and writing a sequence of XML-based commands to the file.
The predefined command files, manage.cmd and nds.cmd, contain predefined transformation templates, which you should not modify.
How does the system know if you are writing a transformation template or the virtual contents of the file? The virtualIO XML element must be written to the file before you send the transformation template. This element is used for many virtual file I/O commands on the admin volume and includes a definition for the behavior of the virtual file.