Web writing is annotation.
Annotations Are the Original Web Writing
The fact that more or less anyone can publish to the web often makes people think that self-publication is its main use. And maybe that is its most common use. But the propleptic visions of Vannevar Bush and Douglas Engelbart, writing in the 1940s and 1960s respectively, remind us of the primary importance of annotations.1
In these early imagined futures of computing, Bush and Engelbart focus on the ability to mark up a document of some sort, the ability to formally instantiate that marked-up document, and the ability to share that with others—each of these three abilities are still fundamental to the way we interact online with text, images, sound, and video. They can also be invaluable aspects of web writing for the liberal arts.
from Web Writing:Why and How.