URxvt.selection.pattern-0: \\|([^|]+)\\|
+Another example: Programs I use often output "absolute path: " at the
+beginning of a line when they process multiple files. The following
+pattern matches the filename (note, there is a single space at the very
+end):
+
+ URxvt.selection.pattern-0: ^(/[^:]+):\
+
You can look at the source of the selection extension to see more
interesting uses, such as parsing a line from beginning to end.