+1 from me. That sounds as a good way to go: just to style the terms with a dashed underline. The link is already generated.

Apart from this, my ideal situation would be

• no explict marking of terms by author like https://training.plone.org/5/contributing/writing-docs-guide.html#glossary-terms
• every appearance ot a term mentionend in glossary is magically fitted with a tooltip.

I gave it a shot, but unfortunately the markup for all links that are internal to the docs use the same class of reference internal.

<a class="reference internal" href="../glossary.html#term-React">
  <span class="xref std std-term">React</span>
</a>

There is currently no parent selector, according to this recent Stack Overflow post.

We can either close this issue as "won't fix", or wait until the standards settle and get adopted by web browsers.

+1 for won't fix (terms get generated link to glossary per default, that's good)
-1 for tooltips for explicit marked terms (marked by directive "terms" https://training.plone.org/5/contributing/writing-docs-guide.html#glossary-terms) and reopen the topic for volunteer that wants to implement

• parsing text for glossary terms
• grab glossary
• fit matched strings with tooltip

There is a new release of https://sphinx-hoverxref.readthedocs.io/en/latest/ that now allows references to non-RTD hosted sites.

https://app.mailerlite.com/b7u3f8

@ksuess what do you think of this implementation? https://sphinx-hoverxref.readthedocs.io/en/latest/usage.html#tooltip-on-glossary-terms

sphinx-hoverxref allows tooltips for glossary terms with no additional markup, just a configuration item. It also allows it for other objects.

@stevepiercy, this looks pretty good, but…. I set it up locally. If I'm not completely wrong, there is a limitation to readthedocs hosting. The tooltip content is loaded as https://readthedocs.org/api/v3/embed/?doctool=sphinx&doctoolversion=4.4.0&url=http://localhost:8000/glossary.html#term-TTW, which fails with 400 error | "External domain not allowed.
The other small minus: A clash with .tooltip of Bootstrap could be solved.

Another approach could be the way collective.glossary will do:
Provide the glossary in JSON format like

[
    {
        "term": "AUTODAT",
        "description": "<p>Automatischer Datenaustausch in Kompass.</p>"
    },
    {
        "term": "Achtung",
        "description": "<p>Nullam quis risus eget urna mollis ornare vel eu leo. Donec id elit non mi porta gravida at eget metus. Aenean eu leo quam.<strong><strong>.</strong></strong></p><h4><strong><strong>Praesent commodo cursus magna, vel scelerisque nisl consectetur et.</strong></strong></h4><p>Fusce dapibus, tellus ac cursus commodo, tortor mauris condimentum nibh, ut fermentum massa justo sit amet risus. </p>"
    },
]

And jquery.glossarizer to automatically markup glossary terms on a page and display definitions as a tooltip.
https://github.com/PebbleRoad/glossarizer

The json could be generate as pre-commit hook?

@stevepiercy, this looks pretty good, but…. I set it up locally. If I'm not completely wrong, there is a limitation to readthedocs hosting.

Oh, bummer, you are correct.

https://sphinx-hoverxref.readthedocs.io/en/latest/installation.html

Warning
This extension requires a backend server to retrieve the tooltip content. Currently, only Read the Docs is supported as backend server. Take into account that your documentation has to be hosted on Read the Docs for this extension to work.

jquery.glossarizer

Are links still clickable? I cannot tell because the demo has # for the href.

It appears that trying to implement sphinx-hoverxref for static sites increases page load times significantly.

• https://docs.red-dove.com/sphinx_sizzle_theme/index.html#tooltips (supported only in the Sizzle theme).

This one actually does not require a server, but the theme itself appears to generate the necessary markup for glossary terms. See:

https://github.com/vsajip/sphinx_sizzle_theme/blob/cf40cd3725b2c578d3029640ae4c28d264addf67/sphinx_sizzle_theme/__init__.py#L576-L603

As a bonus, it could work on docstrings, too, with the use of pdoc to automatically generate a JSON file, as @ksuess mentioned. pdoc appears to work only on docstrings, though, and not glossary terms.

Double bonus: permalinks for Glossary terms. I would love this.