The jobs of theorist and composer have mostly been divided up--few figures in music history are important in both areas. But Messiaen (1908 - 1992) is one of the exceptions. Messiaen wrote a great deal about his technique, especially in Technique de mon langage musical of 1944. Oddly enough, but fitting with the aesthetic of the time, it deals solely with rhythmic, harmonic and melodic technique, excluding any reference to meaning. I say "oddly" because Messiaen was a very spiritual man and the quartet is a prime example. Messiaen wrote that the work was inspired by a text from the Book of Revelation:
And I saw another mighty angel come down from heaven, clothed with a cloud: and a rainbow was upon his head, and his face was as it were the sun, and his feet as pillars of fire ... and he set his right foot upon the sea, and his left foot on the earth .... And the angel which I saw stand upon the sea and upon the earth lifted up his hand to heaven, and sware by him that liveth for ever and ever ... that there should be time no longer: But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished ....The titles of the movements bear this out. One particularly lovely movement is the fifth: "Praise to the Eternity of Jesus". Here is the informative Wikipedia article on the quartet. And here is a complete performance with the score:
The work has a very complex structure, mostly hidden away and only revealed through meticulous analysis. Some techniques, such as isorhythmic patterns, come from the Middle Ages, but others are inspired by Indian classical music and birdsong. There are palindromes, modes of limited transposition (Messiaen's own terminology) and possibly other techniques yet to be discovered! These techniques are not meant to be uncovered by the listener, but are a kind of mystical underpinning to the music.
Our professor in 20th Century Theory and Analysis was waxing lyrical about the piece one day when I had possibly my most brilliant inspiration in graduate school. As he paused, I interjected, "yeah, but, captive audience!"