@MarcoZehe for our timeline control, I was a little on the fence on whether to go with the scrollbar role or the slider role. I decided on the scrollbar role because the control does scroll the page and it does sound like it fits the description given by the W3C:
A graphical object that controls the scrolling of content within a viewing area, regardless of whether the content is fully displayed within the viewing area.
That said, it is a somewhat unique control we’ve built… it both scrolls the page and displays where you are within the current range of posts (so for example it will show you’re currently on post 6 of 12). It’s possible that there’s not a great way to mark it up for screen readers at all, and might be better off hidden… as normal page scrolling works as you’d expect without it. I’d like to give it a try and see what you think of it in action, and if it doesn’t work we can revert.
To answer your question @nolan, I’ve taken on the responsibility of organizing accessibility recommendations and getting our audit done, but most of my previous experience with accessibility comes from implementing specifications defined by others. We don’t have a dedicated expert working on accessibility full-time, as we’re still several orders of magnitude smaller than Slack… but this could be something we need to contract someone to work on in the meantime so we get it right and aren’t making things worse…
Thank you both for your replies, I really appreciate it!