RFC-compliant code is code that follows the formal requirements for the protocols in the TCP/IP stack as specified in a number of RFC ("request for comments") documents published by the Internet Engineering Task Force, aka the IETF. There are many different types of RFC-Compliant requirements, such as HTTP RFC 1945, RFC 2822, RFC 2045, RFC 2046, RFC 2047, and RFC 2231. A complete list of these RFCs can be found here.

Since you requested an example, lets take a look at this Github repository file that builds an OAuth implementation for clients and servers. Specifically, the generate_nonce function. (To avoid copyright / licensing issues, the function will not be posted as part of this answer. Please click the link above to view the file).

Looking at the docstring of generate_nonce, the function "generates a random ASCII-encoded unsigned integral number in decimal representation". Then it shows the specific RFC guideline it's following: . So this function is an example of a piece of code that is RFC Compliant, specifically RFC 5849 Compliant.