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

[This should be a comment, but it would be a very large one!]

I would like to add that %CD% variable is also a special case for the following reason: if a setlocal command is executed and then the current directory is changed, a posterior endlocal command change the current directory back to the one active when setlocal was executed:

@echo off

echo Original: %CD%
setlocal
md newdir
cd newdir
echo In newdir: %CD%
endlocal
echo After endlocal: %CD%

This behavior indicate that %CD% dynamic variable is saved with setlocal's and restored with (explicit or implicit) endlocal's, in the same way of normal variables. However, a weird point is that this mechanism works even if a user CD variable is defined before or after the setlocal! The conclusion is that setlocal command saves the current directory in an area separated from the environment variables, and that endlocal command restore the current directory from that area.