The pipeline is enclosed in curly braces. It consists of one or more 'stages'
separated by commas. Each stage has one or more 'page selectors' (page numbers
or ranges) and an optional list of commands to apply on these pages (separated
-from the selectors by a semicolon).
+from the selectors by a colon).
When a range is written backwards (the first page number is greater than the
second one), the pages are processed in reverse order.