[noise] Handshake pattern rules

[Alex]

What rule(s) describe the ordering of the tokens/message patterns in
section 6? For example, I recall there being concern about a security
flaw if the DH operations are performed in one order or another. What
was the cryptographic reason for that, and are there similar such rules?

The reason I ask is because I want to write code to automatically
validate a given handshake pattern.

-- 
Alex