Thanks for the reply @NoahBoswell! I guess I'm wondering why Canvas hasn't separated the setting for whether mentions are allowed from the setting controlling whether discussion posts can/must be anonymous. It seems to me that those are two separate features, and the instructor (me, in this case) should be able to control them separately - especially when I set discussion to be "partially" (optionally) anonymous posts. As a concrete example, I have a "general questions" discussion in my course where I invite students to post their questions. I want that discussion to be optionally anonymous in case students are feeling nervous about their questions, but if they do post non-anonymously, I would like to "mention" them in my reply, so that they are more likely to get a notification about my reply (depending on their notification settings).