v7 man page for dir

DIR(5)								File Formats Manual							    DIR(5)

NAME
       dir - format of directories

SYNOPSIS
       #include <sys/dir.h>

DESCRIPTION
       A  directory  behaves  exactly like an ordinary file, save that no user may write into a directory.  The fact that a file is a directory is
       indicated by a bit in the flag word of its i-node entry see, filsys(5).	The structure of a directory entry as given in	the  include  file
       is:

       By  convention,	the first two entries in each directory are for `.' and `..'.  The first is an entry for the directory itself.	The second
       is for the parent directory.  The meaning of `..' is modified for the root directory of the master file system and for the root directories
       of  removable  file  systems.   In the first case, there is no parent, and in the second, the system does not permit off-device references.
       Therefore in both cases `..' has the same meaning as `.'.

SEE ALSO
       filsys(5)

																	    DIR(5)