It goes against the unwrittencode in rugby that you don't criticise each other in the media.
Times, Sunday Times (2007)
We were also proposing a change in the unwritten dress code.
Christianity Today (2000)
It is part of Hollywood's unwrittencode: when a star accepts an Oscar, his or her agent must be credited with making it all possible.
Times, Sunday Times (2012)
Definition of 'code'
code
(koʊd)Explore 'code' in the dictionary
countable noun [oft noun NOUN]
A code is a set of rules about how people should behave or about how something must be done.
Definition of 'unwritten'
unwritten
(ʌnrɪtən)Explore 'unwritten' in the dictionary
adjective [usually ADJECTIVE noun]
An unwritten rule, law, or agreement is one that is understood and accepted by everyone, although it may not have been formally or officially established.