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--- /home/albinus/src/emacs-26/doc/lispref/files.texi	2019-03-06 10:39:51.804376822 +0100
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  names.  A file name is a string.  Most of these functions expand file
  name arguments using the function @code{expand-file-name}, so that
  @file{~} is handled correctly, as are relative file names (including
! @file{../}).  @xref{File Name Expansion}.
  
    In addition, certain @dfn{magic} file names are handled specially.
  For example, when a remote file name is specified, Emacs accesses the
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  names.  A file name is a string.  Most of these functions expand file
  name arguments using the function @code{expand-file-name}, so that
  @file{~} is handled correctly, as are relative file names (including
! @file{../} and the empty string).  @xref{File Name Expansion}.
  
    In addition, certain @dfn{magic} file names are handled specially.
  For example, when a remote file name is specified, Emacs accesses the
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  superroot above the root directory @file{/}.  On other filesystems,
  @file{/../} is interpreted exactly the same as @file{/}.
  
+ Expanding @file{.} or the empty string returns the default directory:
+ 
+ @example
+ @group
+ (expand-file-name "." "/usr/spool/")
+      @result{} "/usr/spool"
+ (expand-file-name "" "/usr/spool/")
+      @result{} "/usr/spool"
+ @end group
+ @end example
+ 
  Note that @code{expand-file-name} does @emph{not} expand environment
  variables; only @code{substitute-in-file-name} does that: