Spec Comment od Martin Thomson

This extension helps the developers of standards to collect and manage comments on an active document. It adds controls to the page to allow selecting text for referencing in feedback to specification editors, with support for generating reviews in email, text files, or GitHub issues.

Any HTML document can be annotated, but this has been specially adapted to work with HTML versions of documents from the IETF, W3C, and WHATWG. Using this with other webpages might produce unexpected results.