http://de.selfhtml.org/cgiperl/intro/ssi.htm#uebersicht sollte 'virtual für relative Pfadangaben' verwendet werden und 'file' für absolute Pfadangaben auf dem Server-Rechner.
Das ist Unsinn. Ich zitiere aus
http://www.htmlgoodies.com/beyond/ssi.html :
You use "file=" when the file that will be included is held within the same directory as the file that is calling for it. You can also use the file argument when the file is within a subdirectory of the directory containing the file that is calling for it. This is the one I use every time I create an SSI.
You would use the virtual argument if the file you are calling for is located in a position requiring an address starting at the server root. That's an academic way of saying the file isn't in the same directory as the page that's calling for it.
Gruß
Avalon