A pattern for matching IRC messages. Currently one can only match on the sender or the reciever.

	private-initialization
	sender:recipient:

	filtering	top
	matches: decide whether the message matches this pattern

	private-initialization	top
	sender:recipient:

	instance creation	top
	recipient: create a pattern matching messages to the given recipient
	sender: create a pattern for messages from the given sender
	sender:recipient: create a pattern matching messages from the given sender and to the given recipient