Summer of Protocols

"The purpose of a system is what it does" :: "The purpose of a protocol is what it _______"?

I work for Ethereum at the Ethereum Foundation.

Blogger at ribbonfarm.com, running summerofprotocols.com, host of /gloom ☀️

then maybe: 

"The purpose of a system is what it does" :: "The ________ of a protocol is what it does"?

One of the interesting ideas (see Olivia essay) from SoP was that protocols do not have purposes. Only functions.

The message of a protocol is what it standardizes.

Tend to agree with Venkatesh take.  Though would put  'instructs' personally.