The automake manual already mentions this,
I actually looked in the automake manual first. And the reference I got
to first (don't know why) is the one in the `Program variables' node,
which says "Some variables are inherited from Autoconf". So I went to
the Autoconf manual instead of looking further in automake. Perhaps an
@xref{User Variables}? Perhaps not.
but yes, I agree that adding another sentence in the autoconf manual
can't hurt.
Thanks.
