Looking to @CaseyCarter to confirm cross-ref change is correct, and @jwakely to confirm this change is editorial.

Rather, the reference seems to intend just the [containers.reqmts] subclause, which adds just two useful constraints: random access iterators should support the 3-way comparison operator, and the interoperabiity of container iterators and const_iterators.

If that's the case, there's another place equally affected:

$ git grep -C1 'container iterators' *.tex
containers.tex-\pnum
containers.tex:All requirements on container iterators\iref{container.requirements} apply to
containers.tex-\tcode{span::iterator} as well.
--
strings.tex-\pnum
strings.tex:All requirements on container iterators\iref{container.requirements} apply to \tcode{basic_string_view::const_iterator} as well.
strings.tex-\end{itemdescr}

There's more similarly affected:

$ git grep 'using iterator.*container.requirements' *.tex
containers.tex:    using iterator               = @\impdefx{type of \tcode{array::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{deque::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator        = @\impdefx{type of \tcode{forward_list::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{list::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{vector::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{vector<bool>::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{map::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{multimap::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{set::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{multiset::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_map::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_multimap::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_set::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_multiset::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{flat_map::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{flat_multimap::iterator}}@;     // see \ref{container.requirements}
containers.tex:    using iterator                  = @\impdefx{type of \tcode{flat_set::iterator}}@;  // see \ref{container.requirements}
containers.tex:    using iterator                  = @\impdefx{type of \tcode{flat_multiset::iterator}}@;  // see \ref{container.requirements}
strings.tex:    using iterator               = @\impdefx{type of \tcode{basic_string::iterator}}@; // see \ref{container.requirements}

Yes, would be nice to fix them all.

As a drive-by, fixed the \indexlibrarymember macro by ordering the type, span, before the member, iterator, as is the convention.

Not really; please "grep indexlibrarymember" and you'll see the convention is usually "member, type". Please split this off into a separate commit or a separate pull request if you continue to feel this needs alignment.

There's more similarly affected:

$ git grep 'using iterator.*container.requirements' *.tex
containers.tex:    using iterator               = @\impdefx{type of \tcode{array::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{deque::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator        = @\impdefx{type of \tcode{forward_list::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{list::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{vector::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{vector<bool>::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{map::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{multimap::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{set::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{multiset::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_map::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_multimap::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_set::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator             = @\impdefx{type of \tcode{unordered_multiset::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{flat_map::iterator}}@; // see \ref{container.requirements}
containers.tex:    using iterator               = @\impdefx{type of \tcode{flat_multimap::iterator}}@;     // see \ref{container.requirements}
containers.tex:    using iterator                  = @\impdefx{type of \tcode{flat_set::iterator}}@;  // see \ref{container.requirements}
containers.tex:    using iterator                  = @\impdefx{type of \tcode{flat_multiset::iterator}}@;  // see \ref{container.requirements}
strings.tex:    using iterator               = @\impdefx{type of \tcode{basic_string::iterator}}@; // see \ref{container.requirements}

Actually, these cases are slightly different. Span is not a container, so it is unclear which of the various container requirements are intended to apply. All of these other cases are containers, and the category of container is known, so the whole subclause does apply additional constraints.

I could apply the broader edit if requested, but suggest that should be under a different ticket as the reasoning is more involved.