[pmontra]

Historically reading was kind of a shared experience. Before press "scribes who copied manuscripts often made marginal annotations that then circulated with the manuscripts and were thus shared with the community; sometimes annotations were copied over to new versions when such manuscripts were later recopied" I'm quoting https://en.wikipedia.org/wiki/Text_annotation , references 2 and 3. Interestingly reference 3 is this paper http://jbt.sagepub.com/content/15/3/333 (paywalled PDF, sorry) about the future of annotations.