How to access InstallDirRegKey in NSIS
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I can specify installation directory and registry value in NSIS like this:

    InstallDir "$PROGRAMFILES\CTVI"
    InstallDirRegKey HKLM "Software\CTVI" "Install_Dir"

Now I can access `InstallDir` by using the notation `$INSTDIR` throughout the script. **How do I similarly access `InstallDirRegKey`?** Is there a similar notation as there exists for `InstallDir`? I tried `$INSTDIRREGKEY` but that is not. Now what I do is that I type `HKLM "Software\CTVI" "Install_Dir"` everytime I require it. But that is not so DRY :)