1.
If a committee or organization sets down rules for doing something, it decides what they should be and officially records them.
The Convention set down rules for deciding which country should deal with an asylum request.
= lay down
PHRASAL VERB : V P n (not pron)
2.
If you set down your thoughts or experiences, you write them all down.
Old Walter is setting down his memories of village life.
= write down
PHRASAL VERB : V P n (not pron)