In multi-line CRLF mode (?Rm), the start-of-line and end-of-line assertions match either \r or \n; the current documentation says "and" instead. The use of "and" implies that the full two-byte \r\n sequence is required, but that's not the case; a lone \n still satisfies the assertions, as does a lone \r. "or" makes this clear, and was likely intended; "either $x and $y" doesn't make grammatical sense. You could argue for using "and/or" to emphasize that the assertions do match \r\n newlines, but I think doing so is probably unnecessary and what the "and" could be trying to communicate is much better said by the immediately following clause anyway.

Tested:

[src/main.rs:5:5] Regex::new(r"(?Rm)^$")?.find_iter("\r\r\n\n").count() = 4