Informal briefs

-How is an informal brief created?
An informal brief is created when both client and production company have talk to each other and its never written so everything that is said by both parties isn't certain so both parties have to work by trust.

-What do both parties rely on if undertaking an informal brief?
For an informal brief to work successfully both parties have to rely on trust because nothing is legally written down.
-What does the brief contain?
The brief would contain a quick meetings from both parties they would talk about what they cant and these discussions would usually be noted by both parties. 
-How might the contract be agreed?
after the decisions and discussions are done the verbal contract is usually sealed by a handshake to show trust.

-What are the pros and cons of an informal brief?
the pros of an informal brief is that both parties get to freely exchange what they want from each other and it doesn't have to be written down on a contract but on the other hand the cons of this might be that any of the parties can change their mind or choose not to fulfil their side of the deal and they'll be no consequences for this.