Blanks are optional between operators and strings.
Records are read from the primary input stream. Secondary streams may be defined, but the secondary input stream must not be connected. An input record is written to exactly one output stream when both output streams are connected. It verifies that the sec- ondary input stream is not connected, parses the expression, and then issues a subroutine pipeline to work on data. This subroutine commits to level 0 in due course.