Hi! Thank you for the review and your fixes!

See my answers below.

3. I would rather say to '*an* existing'. Because there is no a one
certain setting to which all the iterators point after setting that
flag.

Thank you, I agree.

4. Even though that bsearch passes the tests, I failed to understand
it. Please, consider a more canonical bsearch on the branch in a
separate commit. Feel free to comment, if someone catches your attention
in my version and you don't agree.

+ if (low < count) {
+ int cmp = strcmp(name[low], key);
+ if ((cmp == 0 && is_including) ||
+     (cmp > 0 && !is_eq)) {
+ *sid = low;
+ return 0;
+ }
+ }

5. This last strcmp can be avoided. Or at least
moved into the cycle. See my commit.

All the same about 'reverse' version.

6. What I don't like here is that we check is_set as many times,
as many modules we have. Moreover, if set_forward didn't find
anything, you fallback to a fullscan in that module, even though
it wont find anything with 100% guarantee.

I fixed it, see my commit.

The thing is that if set_forward fails, then sid = count and next_in_module

will immediately return -1. But if we are going to remove modules, then this

part will be rewritten anyway.

I fixed settings tests also - there was no a check that
real settings space, and a user defined one return the same tuple count. It
could happen, that one of them returns 0 tuples, and it would be considered
success.

Additionally, I added a test, which tries all existing iterators on every
setting.

Thanks, I agree with those.