copygirl

There is something called “local storage” that allows applications to store more information than just a cookie. Cookies are sent to the server, while local storage, as the name implies, stays local. (That doesn’t mean that this data can’t be sent to the server via JavaScript.) But local storage makes it possible to make 100% offline applications if the whole webpage is cached / downloaded (assuming no online functionality is required).

edit: As for deleting this, if I click on the lock icon in the address bar in Firefox, I have an option to clear cookies and site data for the current site. I assume the “site data” is the local storage I mentioned. If you’re using a Chrome based browser, you can probably google how to do the same thing.

From what I read online, Matrix is not very good with its federated moderation tools. Apparently, a quirk of it can cause the state of a federated channel to reset in time, thus also undoing removing of messages. Here is a blog post criticizing Matrix.