Provide an opt-out of the "Terms defined by reference" section

Is your feature request related to a problem? Please describe.

When I reference to a part of another specification with <a data-cite="OTHER-SPEC#section-id">, this entry ends up in the "Terms defined by reference" section, even if the link refers to a section or a table of the other spec, rather than a definition per se.

I understand (from the conversation in #4438) that this is a feature that can not be removed without disrupting some existing documents.

Describe the solution you'd like

As a mitigation, I would like an attribute to explicitly prevent a given <a data-cite=...> to be added to the "Terms defined by reference",
for example following @gkellogg's suggestion:

It would be nice to have something like which could be more granular than data-link-type="heading", but both would solve this specific issue. For specs that really don't want to consider referenced terms as being "defined by reference", they could either use this pattern universally, or do something like `, if that would also keep it out of the index.

Describe any alternatives you've considered

An obvious alternative would be to replace data-cite="OTHER-SPEC#section" with href="real-url", but it kind of defeats the purpose of using Respec...

Can you or your organization fund the work or help with development?

unfortunately not.

Start by tracing how data-cite links are processed and how the "Terms defined by reference" section is generated, using the behavior discussed in issue #4438 as context. The work is done when an explicit opt-out prevents a referenced section or table from appearing there while existing data-cite behavior remains unchanged.