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Em-Dash Highlighter Browser Addons
(lemmy.ca)
While interesting—in a curious sort of way—I think it will simply reveal that a whole lot of stuff on the Internet has been automatically replacing dashes with em dashes for a long time. Also, a whole lot of professional writers have been using it since forever.
A better "aha! AI!" catch is post-2020 usage of emojis as bullet points. Though, that really only catches ChatGPT and Claude (Gemini and the other models don't do it as much unless they know they're making a README.md).