The rules of assembly society (sangha) include the way of self-cultivation personally,the way of interaction of whole community,and their social sense. The learning of dharma, by which one can become a monk within dharma, is the three increased studies of learning (discipline,meditation,and wisdom). As the manner and behavior in ordinary life is considered,thereby the learning is indeed a worthy learning,which is the unwritten rules or laws in the light of embodiment of Buddha.
There are two principles in the life of community,i.e. "the doctrinal unity in views and explanations" (to feel the taste of Buddha's truth with others) and "the economic unity in community of goods" (to share the offerings with others). Both of them are of the six points of reverent unity in amonastery.
The formation of learning of discipline has three stages:the four all-embracing virtues, the full commands of disciplinary process, and the achievement of discipline. The final stage is the formal "discipline" of Buddha's teaching,the others are "converting" (stages of enlighnment). We may call the converting as "customary laws."
The transform from convertings to discipline is based on many accomplished fact,which are consistently used as rules as well as those rules are admitted sequentially by the whole community. Even so,sometimes the customary laws still support the written laws, which are originated from the former. In other word,the written laws modify at all times when they under an actual circumstance. Similarly,the rules of assembly society -- the discipline may be suited to the new condition.