by an expression which is often a variable name; the control expression or control variable.

; Cases: Subsequent branch alternative sections each start with a keyword (i.e. ) plus a value (or multiple values) along with code to execute for the value(s). In some languages, i.e. PL/I and Rexx, if the control expression is omitted then each alternative begins with a clause containing a Boolean expression and a match occurs for the first case for which that expression evaluates