+sub-expression so that it will indeed float.
+
+If you can float to level @Level 0 0@ worth doing so because then your
+allocation becomes static instead of dynamic. We always start with
+context @Level 0 0@. @InlineCtxt@ very similar to @Level 0 0@, but is
+used for one purpose: to say "don't float anything out of here".
+That's exactly what we want for the body of an INLINE, where we don't
+want to float anything out at all. See notes with lvlMFE below.
+