Deryniness itself is actually a complex set of genetic keys that unlocked various abilities inherant in most people. Some are dominant traits, others recessive. A few talents even depend on the presence of a series of genetic keys. Healing is one such talent and the blocking of powers is a further subset of the healing ability.
There are also two "master" keys. Each is sex linked. The X' key is common in almost all deryni and is very easy to detect in even the youngest children. This key automatically activates itself, unlocking any basic skills present in the child. The Y' key is more difficult to detect, but potentially much more powerful. The Y' key not only unlocks the full deryni potential, it also decodes RNA messages and allows the man with these powers immediate access to whatever deryni powers were included in the "unlocking" ritual.
It is also possible to have deryni powers without one of these "master" keys. A person can be born with enough specific keys to specific areas to unlock a few specific talents. Truth reading requires only a few of these specific keys, and does not require all be present to unlock parts of the talent. Healing requires several keys and if even one is missing, the talent will be blocked.
Most Deryni ritual developed around the four basic physical elementals, Air, Fire, Water, and Earth. Each of these has a direction and a color associated with it as well as a domain. Archangelical personifications were added after the diaspora when Deryni had to blend in with the Judeo-Christian-Islamic religions becoming prominent on the mainland. Air is associated with the east and healing, and is represented by the color gold and Archangel Raphael. Fire is associated with the south and defense, and is represented by the color red and Archangel Michael. Water is associated with the west and communications, and is represented by the color blue and Archangel Gabriel. Earth is associated with the north and death, and is represented by the color green and Archangel Uriel. Caeriesse sported four collegia, each dedicated to one of these elementals. Three of these four "Seats" were located on the Caeriessen central plain. Only the Air Seat was located in the southern slopes of the northern barrier ridge.
When the island sank, only the leaders of the Air Seat survived, and the only writings to survive were the few texts journeman level students took with them on the ships.
There are also three esoteric elementals represented in some ancient Deryni lore. They are basically Good, Evil, and Balance and are associated respectivly with white, black, and purple. Because most of this lore was lost when Caeriesse sank, Archangels were never associated with these, but the ancient gods were Gaea, Loki, and Fate. All of the writings associated with these elementals were lost. A few surviving scholars tried to reconstruct what they could from memory, but the effort to survive and build new lives on the mainland often interfered. The most ironic thing about these three esoteric elementals is the fact that the powers associated with them are present in all but the very youngest Deryni children. In fact they aren't truly Deryni powers at all. They are, instead, the Deryni equivalent of each person's guiding "voices" and the power of compromise.
There are several talents that are unlocked only by their specific keys. The primary healing function is only one of these. Each of the four domains, healing, defense, communication, and death have their own keys, and all of these keys must be activated. This activation can take the form of a ritual, but more often responds to a situational trigger. While a few functions associated with each of these areas could possibly be available to many deryni, the full potential will be available only to those few deryni who posess all of the keys for the series.
By the time of King Kelson almost everyone probably has some of the Deryni keys in their genetic makeup. This allows the development of "rogue" talent like Warin and Derry. It also accounts for the "second sight" in the border folk. The four physical elementals figure heavily in Deryni ritual, but the three esoteric elementals are almost forgotten. Almost, but not quite. They are still represented in several small ways. The seven windows of the Duke's tower at Coroth, and the seven points on the Corwyn Ducal Coronet are a small sample that they are not completely gone.