Proposed feature for Safari: Markup.

Highlights and notes, with Pencil support, as an overlay atop the original page. Personal, not public, but synced via iCloud. I’d use this every day.

@gruber We actually prototyped something like this over a decade ago but we didn't think anyone but you would use it.
@donmelton @gruber As a product person who would also use this on a regular basis, it always shocks me when a new browser includes fancy screenshot and sharing tools. (Lookin’ at you, Arc.)