A
keyword instruction is one or
more clauses, the first of which starts with a keyword that identifies
the instruction. Keyword instructions control the external interfaces,
the flow of control, and so forth. Some keyword instructions can include
nested instructions. In the following example, the DO construct (DO,
the group of instructions that follow it, and its associated END keyword)
is considered a single keyword instruction.
DO
instruction
instruction
instruction
END
A
subkeyword is a keyword that is
reserved within the context
of some particular instruction, for example, the symbols TO and WHILE
in the DO instruction.