The Commission of the Realm is the highest assembly in the land, and is able to exercise full royal authority in the case of incapacity of the king, or when delegated to do so.
The Commission only exists formally as such when required to meet to consider some matter. Typically this is when the king is indisposed for some reason — in the extreme case, if deceased, without heir of age of majority, or duly appointed regent. Alternatively, the king may command it to meet for some purpose. The same or a similar group of people is often summoned to advise the king, though strictly, legal theorists insist, this is a “High Council”, rather than the Commission as such.
The Commissioners are generally also High Officers of State. The distinction between the two is that the commission has all the powers of the king, but only exercises them collectively, while officers have specified, restricted powers, but exercise them by themselves. Because the prestige of the Commission, such officers are often still referred to as “Royal Commissioner”, even when acting as counselors or officers.
The composition of the Commission has varied considerably. In theory appointments are made by direct royal command, and might be of any person, regardless of other position or rank. However, because it is often required to meet in times of unexpected contingency, various precedents have evolved regarding which office-holders attend. Typically, where an individual or holder of an office was summoned to the last commission, or a royal decree was in the interim issued to such an effect, that that person, or the holder or the same office, will be a member of the next Commission. Ambiguity and disputes have arisen on this matter, however.
The roles of many of the offices have varied over time, some seemingly (or actually) overlapping with others. Some have little remaining practical purpose, and exist mainly to signify the importance of the holder at court, or indeed to establish the right of that person to sit on the Commission. A single person can simultaneously hold several positions, and some have been combined as a matter of custom. Various positions have been removed from the Commission, or left unfilled.
Not all of the following would be on the Commission at any one time, and exact titles have varied over time.
Normally no royal person sits on the Commission, as they instead exercise power in their own right, though often essentially the same body meets to provide counsel rather than make executive decision. On occasion, however, the Commission is vested with co-regency powers, in which case it sits with the Crown Prince (or other regency) at its head.