Nextcloud Files sidebar tabs

Describe why it is important and where it will be useful

Context

Hi, I tried to use an ExApp to implement a tab for the Nextcloud Files sidebar (details tab, like Activity and Sharing) and wasn't able to get it working. I looked at the relevant docs, many examples and source code, but didn't find the combination ExApp + Files sidebar tab as an example.

Here is the Nextcloud Forum post for some context:
https://help.nextcloud.com/t/sidebar-tab-in-files-with-exapp/224280/10

As you can see in the post, kyteinsky suggested there might be some functionality missing in app_api to make this possible and a feature request (or PR) would be the way forward.

Why is this important?

I think it would be good, if the App API would make the same types of apps and additions possible, that regular Nextcloud apps make possible.

Describe your proposed solution

Implement the missing features to make sidebar tabs implementable, analogous to TopMenu and other types of frontend scripts.

Describe alternatives you've considered, if relevant

For my concrete project, I could use other solutions, but a sidebar tab would be the most elegant.

Additional context

I would like to help implement this, but unfortunately I'm not very experienced with PHP and Nextcloud. Also thanks in advance.

Start by reading the AppAPI documentation, examples, and source code for TopMenu and other frontend scripts, then compare how regular Nextcloud apps add Files sidebar tabs. Use the linked forum discussion for context and define done as enabling an ExApp to implement a Files sidebar tab analogous to a regular app.