>> Can you prepare a PR against Harold's repo, at least for the document? 

Sure.

> Note scsh has procedures to do this, in the currently "Intentionally
> omitted" section 3.11:
> https://scsh.net/docu/html/man-Z-H-1.html#node_toc_node_sec_3.11

Thanks.

scsh uses the names "getenv" and "setenv", as does Gambit. Gauche has
"sys-setenv". Chez has "putenv". I guess "set-environment-variable"
would be an appropriate name for SRFI 170 since that would match R7RS
and SRFI 98.

Should we have a separate "delete-environment-variable"? Alternatively,
(set-environment-variable "FOO" #f) could ensure the variable is
removed. That would match (get-environment-variable "FOO") which returns
#f if FOO is not defined.