Conditional execution of actions.

Expression1, expression2, ... are evaluated in successive steps. When one of the expressions gains the value TRUE, then actions following this expression are to be executed up to the nearest ELSIF, ELSE or ENDIF. If any of the expressions does not gain the value TRUE, then the sequence of actions between the commands ELSE - ENDIF (they are optional) is to be executed.

If some of the expressions expression1, expression2, ... gains an invalid value, the action generates the error _ERR_EXPRESSION_STATUS.

An equivalent of the action IF THEN [ELSIF] [ELSE] ENDIF may be coded using the conditional jump IF GOTO and the action GOTO. The advantage of the action IF THEN [ELSIF] [ELSE] ENDIF is that there is no need to create labels and their names (it increases the code transparency).