RFC2045 is the “main” MIME document, and as such, one would imagine that there would be a lot to implement. But there isn’t, since most of the implementation details are delegated to the subsequent RFCs.
So rfc2045.el has only a single function:
rfc2045-encode-string ¶Takes a parameter and a value and returns a ‘PARAM=VALUE’ string. value will be quoted if there are non-safe characters in it.