unwritten rule

Wall Street has a hard-fast unwritten rule about compensation: Don't ask, don't tell.

The unwritten rule of luxury goods marketing is to rise above the messiness of the moment.

The unwritten rule of the prison camp is, whatever one gets the rest all share it, so they were disappointed too.

This was not a decision adopted to meet the special case in hand, but rather an unwritten rule of the community.

Mund halten (keep your mouth shut) is the unwritten rule, and every one seems to observe it strictly.

It is part of the unwritten rule of circus business to ignore fear and panic.

I found, later on, that there is another unwritten rule, but I think that belongs solely to the West.