>> I looked into how that library is actually used later on, and it turns
>> out it's in only one function in private/chibi-sxml.scm, and that only
>> a use of the let-optionals macro that would have worked with the more
>> limited version that comes in Chicken's core library. Oh well. It was
>> educational, at least.
>
> Right. If that's the only place, my vote is to patch our copy of
> chibi-sxml not to require the SRFI.
>
> The downside is that each upstream release of chibi-sxml will have to be
> patched, but that library is quite stable and probably won't get many
> essential upgrades.

I suggested to Alex (who wrote chibi-sxml) to manually unroll the
optional arguments parsing for that library and he said it's fine. The
patch has now been mainlined:
https://github.com/ashinn/chibi-scheme/commit/561fc1bae083f98e02a5e696c5be13c9f4d0c4bd
If we upgrade the copy in the srfi-tools source tree, that solves the
immediate problem.