This variable defines a series of directories to be searched for data files.
The value "." is the default.
You can specify a directory path that contains embedded spaces if you surround
the path with quotation marks. For example:
FILE_PREFIX C:\"Sales Data"
Remote name notation is allowed for the FILE_PREFIX variable if your runtime is client-enabled (for indexed files, remote name notation requires the Vision file system). Up to 4096 characters can be specified for the value of this variable.