Possible Clues:

• The rules for gear selection?
• Stipulated attire
• "No jeans" may be part of one
• The rule for making a sporting selection?
• Set of rules which may mean men are 'tied'?
• Reason why a restaurant might keep a supply of jackets
• 'Add vinegar etc to fish' : Jamie's ultimate restaurant rule?
• Casual Friday relaxes it
• Convention governing clothes to be warn on a particular occasion
• "No shoes, no shirt, no service," for one