Enable markdown attributes for dt elements

[jmooring]

This markdown:

term
: definition

is currently rendered to:

<dl>
  <dt>term</dt>
  <dd>definition</dd>
</dl>

but what I really, really want is:

<dl>
  <dt id="term">term</dt>
  <dd>definition</dd>
</dl>

This would allow us to manually link to the term, which would be very useful on documentation sites, our documentation site in particular.

ID's should be assigned using the same logic as heading id's... use GitHub id format, and increment as needed to prevent duplicates on the same page (that means checking heading id's as well).

Other thoughts:

• Should this have an on/off switch? I can't think of a reason to disable the functionality.
• If we do this, at some point someone will want to override the id using a markdown attribute, like you can with headings. But we can't currently assign a markdown attribute to a list item, only to the list itself.
• This could also be handled (sort of) with a markdown render hook (layouts/_default/_markup/render-dt.html), but you wouldn't have the ability to guarantee unique ids (the render hook would have no knowledge of other id's on the page).
• At some point these could be added to the .Fragments map as well (perhaps useful for .Related).
• You can use this link render hook hack, but the markdown isn't portable.

Reference: https://discourse.gohugo.io/t/automatically-add-id-attribute-to-dt-element/38191

[dvdksn]

instinctively I'd expect this to be configurable via markup.goldmark.parser, like heading IDs are. And that the strategy for generating these IDs are controlled the same way.

[bep]

Is is possible to do:

term
: definition
{#term}

?

Not saying that it's great, but then again, having stable IDs have its benefits.

[dvdksn]

@bep that would add the ID to the <dl> element

[Winterhuman]

I'd also want some form of toggle for the ID behaviour, purely for the sake of not needing them, but also because the content of <dt> elements isn't necessarily always short enough to be appropriately put into an ID value (since it can be used generically as a key-value store per its semantics).

(A render hook would be appreciated)

[jmooring]

Thinking about this more, adding the ability to set markdown attributes on dt elements is probably the best way to handle this. For example:

Term A {#foo}
: Description of Term A
Term B {#bar}
: Description of Term B

Notes:

• Automatically adding an id attribute to every dt element might be something to consider in the future.
• On the doc site we (I) are currently hijacking h6 elements to make them look like dt elements.

[bep]

I have added auto ID support for dt in #13404 -- I agree that it would also be nice to be able to manually override these IDs, but that needs to be implemented in the upstream extension:

https://github.com/yuin/goldmark/blob/d9c03f07f08c2d36f23afe52dda865f05320ac86/extension/definition_list.go#L29