Reference/.onVerifyInstDir
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.onVerifyInstDir
This callback enables control over whether or not an installation path is valid for your installer. This code will be called every time the user changes the install directory, so it shouldn't do anything crazy with MessageBox or the likes. If this function calls Abort, the installation path in $INSTDIR is deemed invalid.
Example:
Function .onVerifyInstDir IfFileExists $INSTDIR\Winamp.exe PathGood Abort ; if $INSTDIR is not a winamp directory, don't let us install there PathGood: FunctionEnd