I recently encountered an answer that does nothing but refer to the poster's book:
Please look pages 141-147 of the book:
S. Saitoh and Y. Sawano, Theory of Reproducing Kernels and Applications, Developments in Mathematics 44, Springer (2016). 2023.5.4.20:36
This answer was posted by S. Saitoh. Also, literally 100% of this poster's answers across multiple sites in the Stack Exchange network promote the author's books and/or papers, and the account has had multiple spam flags upheld against it on multiple sites.
However, the spam flag on this answer was declined as having no evidence to support it. Why was this not considered spam?