So you all know that the package name xaringan was from Sharingan in Naruto. Sharingan means really, really good eyes. Earlier this month, I stumbled upon a Stack Overflow question on xaringan, and was amused after seeing its answer by Yue Jiang. The OP was asking why the slide separator --- didn’t work as expected but generated a horizontal rule instead.
It turned out there was a trailing space after ---.
Apparently, Yue Jiang (Uchiha?) is a qualified ninja with Sharingan.
That was not the end of the story, though. There was a much longer story behind these three dashes. If you have too much time to kill, you may read through the GitHub issue yihui/xaringan#151.
Once again, we love software. Don’t we?
BTW, I believe Emi Tanaka also has Sharingan, since she discovered the greatest power of xaringan::inf_mr() (i.e., the “Infinite Moon Reader”): it preserves the scroll/navigation position when automatically refreshing the page!