Will Robertson wrote:

> Sounds like a good read for people like us to start using expl3 and
> help to stabilise it as soon as possible! Changes in expl3 are only a
> problem when we stop maintaining existing code. And I hope that after
> a (relatively) short time of practical use in "our" packages, the
> basic interface will be good enough to freeze.
> 
> After all, we *want* to start using this stuff, right?! So it's in our
> interests to get it in a state whereby that is possible.

Of course.  I might look at something on siunitx on the basis that
"things are close to done on the low-level side".  I've been having
various thoughts in that direction in any case.  (First, though, I have
to finish v1.1 of the current release!)

> (This reminds me of an interesting versioning idea: is it worth adding
> hooks in the package loading code so that when a user requests a
> specific version, the package is able to fall back on its old
> behaviour? Like an implicit "compatibility" switch. Something like
>   \IfOldPackageDate{2006/06/08}{...implement old functionality...}
> )

An interesting idea, but gets very complex very quickly (if one makes
more than a trivial number of changes).
-- 
Joseph Wright