Full path:
   an existing file                 C:\winnt\t1.txt         o.k
   a not existing file              C:\winnt\t1notex.txt    FO() dialog with C:\winnt
   a not existing directory         C:\xMM\t1notex.txt      FO() dialog with CWD
   invalid character in filename    C:\windows\t1:xx.txt    error (o.k.)

relative path from CWD (buffer not assigned to a file):             
   an existing file                 test\dir1a.txt          o.k
   a not existing file              test\dir1anot.txt       FO() dialog with CWD\test
   a not existing directory         not\t1notex.txt         FO() dialog with CWD
   invalid character in filename    test\dir:1a.txt         error (o.k.)

relative path from loaded file:
   an existing file                 old\projsave.vdm        o.k
   a not existing file              old\projnotex.vdm       FO() dialog with filedir\old
   a not existing directory         not\t1notex.txt         FO() dialog with CWD
   invalid character in filename    old\proj::save.vdm      error (o.k.)
   
no path:
   an existing file                 t2.txt                  o.k
   a not existing file              t2notex.txt             FO() dialog with CWD
   invalid character in filename    t2:::test.txt           error (o.k.)