leading and trailing spaces are trimmed.
If the type of the parameter specifies it, access mode checks are done
on file. So if access mode specifies write mode, and the file is read-only
then PILGetFname will not accept that filename
and will prompt user to enter name of the file which is writable.
Before applying any checks the value of the parameter (which may be URL,
for instance http://, file://etc/passwd) is converted to the filename
(if it is possible). Details are given in paragraph .