In the Wise installer's "Advanced Options" dialog, substitute in the
actual name of "the system directory" -- this is clearer, and especially
for people reading this dialog who aren't me <wink>.

until you download the new expat and install it; see PCbuild\readme.txt.

extensions -- but Inno uninstall doesn't restore previous ones (if any),
so that's another step backwards.

parts Inno has no good answer for (read the comments at the top of the
script).