Why can't I access a variable named __CD__ on Windows 7?

Question

Note - this question is based on behavior observed on Windows 7. I believe the behavior applies to all other versions from Vista onward. Based on MC ND\'s answer, and Fo

Answer 1

According to this command line reference there are read-only environment variables, where __CD__ is included.

From that page:

Undocumented Dynamic variables (read only)

%__CD__% The current directory, terminated with a trailing backslash.

%=C:% The current directory of the C: drive.

%=D:% The current directory of the D: drive if drive D: has been accessed in the current CMD session.

%=ExitCode% The hex value of the last return code set by EXIT /B

%=ExitCodeAscii% The ASCII value of the last return code set by EXIT /B if greater than 32.