Birtwistle's opera consept

I ran into this text about Birtwistle's opera "Gawain" and found it very interesting. I'm pasting it here so I don't forget to read it again.

Birtwistle's method of working is also reflected in the events of the first Act of his opera Gawain. Up to the point where the Green Knight is kneeling in front of Gawain awaiting the axe blow that will cut off his head, the action has proceeded mainly in chronological order. With Gawain holding the axe aloft, the stage is suddenly blacked out and, within a minute, the action has been rewound to the point preceding the Green Knight's entry to the Court of Arthur. Events are played through again, though compressed and with various small alterations, through the beheading and into the subsequent events. The events on stage are not randomly ordered, but the one event is portrayed from more than one perspective.

For the opera The Mask of Orpheus, this entailed two sets of singer/actors performing contradictory versions of the one event from the Orpheus myths. This non-linear portrayal of events on stage gives the listener a means of approach to the abstract compositions, with the same musical ideas being repeated but with extensive variation. The result is music that is often very episodic in structure. A clear example occurs in Silbury Air in which a readily identifiable musical motif – a blow from the tom-toms followed by scurrying figures from the strings and woodwind – is elaborated in a number of different ways as the piece progresses.

-Taken from wikipedia
http://en.wikipedia.org/wiki/Harrison_Birtwistle