HTTP Method Names: Upper or Lower Case?

This might be an autoresponder question, but I hope one of you can point me to any resource where it is declared or inferred whether to use uppercase or lowercase letters when declaring an HTTP method name in HTTP or REST. Most of the examples I see put GET, PUT, POST, DELETE, PATCH, etc. In all caps, whereas I am assuming that HTTP method field names are case insensitive — that is, for example, "get" is equally valid as "GET". Traditionally, I've always used capital letters, but I just wanted to be sure.

The W3C explicitly declares that the method is case sensitive and uses upper case, but in my agony I often came across the HTTP method field value used in lower case, which I assume is incorrect, so from my POV it seems that the practice and standards somewhat do not address this issue.

Is the upper case correct - correct?