[[What is the purpose of this Windows environment variable and how does it impact Tcl?]]

[MHo]: COMSPEC holds the path to the current command processor (command shell), which is something like '''c:\windows\system32\cmd.exe''' on modern windows versions. On Windows 9.x, the command shell is '''command.com''' instead of '''cmd.exe''', which is a relict from 16bit-MSDOS-days (still present for compatibility reasons). Programs could (and should) shell/exec to env(comspec) instead guessing what the command processor is ;-) I don't know how this envvar is used tcl-internally...