I've collected some examples regarding possible widgets:

1. Image + text

2. Text

3. Image + text + user + last edit info

4. File preview + text

5. Gif + text

6. Edit mode of existing internal document

Some examples which are not workable in other apps:

1. Youtube (image)
   

2. Code snippet form Github:

3. Any info from Github:

@JuliaKirschenheuter in the popover widget (not the directly embedded one) the title is always duplicated, can we get rid of that?

(If it is needed as a placeholder until the actual widget loads that could be done but then replaced with the widget.)

As discussed via chat, the scope of this issue is to provide metadata for notes app links like https://nextcloud.local/apps/notes/note/12345 using the existing link preview API, so instead of the odd placeholder in the first post we'd show the note title somehow similar to linking a file maybe.

@jancborchardt Your comments seems a general text issue, maybe that can be filed separately (with a reference screenshot).

Thanks for the great screenshots of references @JuliaKirschenheuter ! Very helpful!

I would suggest it be like in Collectives, so (3) looks great. The image can be the file thumbnail. The text can be the name of the note on the first line, in [name of category] on the second line (if it is categorized), and last edited on the third line.

With the standardization of the widgets the specifics of the size, width, etc can be smoothed out in the other issue :)

Seems that backend have to be implemented first. https://docs.nextcloud.com/server/latest/developer_manual/digging_deeper/reference.html#register-a-reference-provider (ReferenceProvider, PublicReferenceProvider) and https://docs.nextcloud.com/server/latest/developer_manual/digging_deeper/reference.html#using-the-default-widget for default widget (should be enough for current task).

Could this implementations serve as examples?:
https://github.com/nextcloud/spreed/blob/main/lib/Collaboration/Reference/TalkReferenceProvider.php#L109
https://github.com/nextcloud/deck/blob/main/lib/Reference/BoardReferenceProvider.php
https://github.com/nextcloud/richdocuments/blob/main/lib/Reference/OfficeTargetReferenceProvider.php