technical documentation as RFCs, an acronym for their historical title *Requests for Comments*. They define the Internet's technical foundations, such as addressing, routing and transport technologies. They recommend operational best practice and specify application protocols that are used to deliver services used by billions of people every day. RFCs are freely available and software developers, hardware manufacturers, and network operators around the world voluntarily implement and adopt the technical specifications described by RFCs.” About RFCs
in a URI but do not have a reserved purpose are called unreserved. These include uppercase and lowercase letters, decimal digits, hyphen, period, underscore, and tilde.” unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" RFC 3986におけるアンダースコアの扱い