specifies the fileref
to be validated. Under Windows, fileref can also be a Windows environment variable. The fileref or the environment
variable that you specify must be enclosed in quotation marks.
Details
A negative return code
indicates that the fileref exists but the physical file associated
with the fileref does not exist. A positive value indicates that the
fileref is not assigned. A value of zero indicates that the fileref
and external file both exist.