In general, the vtables for the different chains will have \emph{different}
structures.
-The instance layout split neatly into disjoint chains. This is necessary
+The instance layout splits neatly into disjoint chains. This is necessary
because each @|ichain| must have as a prefix the @|ichain| for each
superclass in the same chain, and each slot must be stored in exactly one
place. The layout of vtables doesn't have this second requirement: it
~mdw / sod / blobdiff