i know in my relationships i have had assorted items that have been required or requested. Would i call them rules... some yes, some no. Either way it was what worked for U/us and kept growing and changing as W/we grew and explored together... Sometimes additional items being added, other time items being dropped. Just what ever worked for U/us at that time.
Personally... i think the important thing to remember is that each relationship will have their own set of rules for what works for that relationship. Just as no ones kinks are the same no one's rules are the same either. And, i have seen situations where one Dom/me with 2 (or more) subs may have different rules for each sub... because that is what worked for the relationship and most importantly for the subs involved.
And everyone's definition of what a "rule" is will vary as well. Some may see a standing request as just that a request and not a "rule" where as to others that is a hard and fast "rule." i'm not sure i can define any certain "rule" although i know i have had to meet set expectations...
Different kinks... different rules... different definitions... fun for those involved! That is what's important!
Just my two cents worth....