Tom Scott has a nice intro video about this: ▶ this video The book he mentions, Because Internet, goes into more detail. But to over-simplify, there were a few major generations of people joining the internet as well as a generation that never fully joined, and each one developed its own conventions for casual writing on their own. Some used the same mechanism to mean different things.
in “A case for using punctuation in Slack” · View on HN