upward compatibility

[DILL at CMU-20C]

I believe that compatibility with other lisp dialects should be a
consideration in the design of Common Lisp, but it should absolutely have
less priority that considerations of portability, taste, and efficiency.
It is possible that this won't leave a whole lot of room for upward
compatibility.

If Common Lisp manages to be a high-quality, widely implemented common
language, the user community will end up being much larger than that of
any existing lisp dialect.  Imposing misfeatures on those users because
a much smaller community of users has gotten used to those features
doesn't make sense.

I also don't see why it is more important to maintain compatibility with
Maclisp than with other dialects.
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