Delayed environment variable expansion is NOT enabled by default.  You
can enable or disable delayed environment variable expansion for a
particular invocation of Cmd.exe with the /V:ON or /V:OFF switch.  You can
enable or disable completion delayed expansion for all invocations of Cmd.exe
on a machine and/or user logon session by setting either or both of the
following REG_DWORD values in the registry using RegEdt32.exe RegEdit.exe:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\DelayedExpansion

        and/or

    HKEY_CURRENT_USER\Software\Microsoft\Command Processor\DelayedExpansion

to either 0x1 or 0x0.  The user specific setting takes precedence over
the machine setting.  The command line switches take precedence over the
registry settings.

If delayed environment variable expansion is enabled, then the exclamation
character can be used to substitute the value of an environment variable
at execution time.

File and Directory name completion is NOT enabled by default.  You can
enable or disable file name completion for a particular invocation of
Cmd.exe with the /F:ON or /F:OFF switch.  You can enable or disable
completion for all invocations of Cmd.exe on a machine and/or user logon
session by setting either or both of the following REG_DWORD values in
the registry using RegEdt32.exe RegEdit.exe:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\CompletionChar
    HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\PathCompletionChar

        and/or

    HKEY_CURRENT_USER\Software\Microsoft\Command Processor\CompletionChar
    HKEY_CURRENT_USER\Software\Microsoft\Command Processor\PathCompletionChar

with the hex value of a control character to use for a particular
function (e.g.  0x4 is Ctrl-D and 0x6 is Ctrl-F).  The user specific
settings take precedence over the machine settings.  The command line
switches take precedence over the registry settings.

If completion is enabled with the /F:ON switch, the two control
characters used are Ctrl-D for directory name completion and Ctrl-F for
file name completion.  To disable a particular completion character in
the registry, use the value for space (0x20) as it is not a valid
control character.

Completion is invoked when you type either of the two control
characters.  The completion function takes the path string to the left
of the cursor appends a wild card character to it if none is already
present and builds up a list of paths that match.  It then displays the
first matching path.  If no paths match, it just beeps and leaves the
display alone.  Thereafter, repeated pressing of the same control
character will cycle through the list of matching paths.  Pressing the
Shift key with the control character will move through the list
backwards.  If you edit the line in any way and press the control
character again, the saved list of matching paths is discarded and a new
one generated.  The same occurs if you switch between file and directory
name completion.  The only difference between the two control characters
is the file completion character matches both file and directory names,
while the directory completion character only matches directory names.
If file completion is used on any of the built in directory commands
(CD, MD or RD) then directory completion is assumed.

The completion code deals correctly with file names that contain spaces
or other special characters by placing quotes around the matching path.
Also, if you back up, then invoke completion from within a line, the
text to the right of the cursor at the point completion was invoked is
discarded.

The special characters that require quotes are:
    
     &()[]{}^=;!'+,`~

GuardNotes

Things that are different (by design, by accident or otherwise)

...