A keyword instruction is one or more clauses, the first of which starts with a keyword that identifies the instruction. If the instruction has more than one clause, the clauses are separated by a delimiter, in this case a semicolon (;).
Some keyword instructions, such as those starting with the keyword DO, can include nested instructions.
In the syntax diagrams, symbols (words) in upper case letters denote keywords; other words (such as expression) denote a collection of symbols. Keywords are not case dependent: the symbols if, If, and iF would all invoke the instruction IF. Also, you usually omit most of the clause delimiters (;) shown because they are implied by the end of a line.