The nsIRelativeFilePref interface is a wrapper for an nsILocalFile and
 and a directory service key. When used as a pref value, it stores a
 relative path to the file from the location pointed to by the directory
 service key. The path has the same syntax across all platforms.

 @see nsIPrefBranch::getComplexValue
 @see nsIPrefBranch::setComplexValue
[scriptable, uuid(2f977d4e-5485-11d4-87e2-0010a4e75ef2)]
interface nsIRelativeFilePref : nsISupports

Attributes

 file

 The file whose location is stored or retrieved.
attribute nsILocalFile file 
 relativeToKey

 A directory service key for the directory
 from which the file path is relative.
attribute ACString relativeToKey