Consider allowing the HTML <details> tag in messages

[ananace]

As noted in #twim:matrix.org, bot output can easily become quite large, to the point where a simple user response fills an entire screen and breaks conversation.

To offer a way to avoid this, without losing legibility or having to remove important information from bot responses, perhaps supporting the HTML <details> tag could be a solution. Tag references; <details>, and <summary>.
The contents of the details - and the associated summary - block would of course be subject to the normal Matrix tag rules.

I can see many places where the ability to offer both a summary and a detail view in the same message could be of huge help to bots. From RSS feed or commit updates - where a message could contain the title and link as a summary, with an excerpt as the details - to monitoring alerts where the summary could be the alert itself, and the details would contain relevant graphs or full check outputs.