I'm not entirely sure that these fully answer the questions you're asking, but: - The annotations get "anchored" to the text in place at a given URL. There's

I'm not entirely sure that these fully answer the questions you're asking, but: - The annotations get "anchored" to the text in place at a given URL. There's a video online of Rap Genius [née Genius] discussing fuzzy annotation anchoring [1]. I would guess Hypothesis does something similar. Also, their client code is on GitHub. - Annotations can be replied to but as far as I know there is no mechanism for voting or any one particular annotation being more trusted than others. The site owner could make an official group for their site I suppose. - The underlying page can be modified at any time. If something is annotated and that underlying text is significantly changed or removed, the annotation becomes "orphaned" and shows in a separate area. If you really want to, you could archive the page first with e.g., archive.is and then annotation an archived version. - I do think that Hypothesis maintains an archived version of an annotated page, or at the very least the portion of its text which you've anchored annotations to so that you can view them outside of the context of the page. [1]: https://www.youtube.com/watch?v=FJyqfRcyYIQ https://www.youtube.com/watch?v=FJyqfRcyYIQ