Flow

This optional parameter can be used to create an expression which is not a flat list of expression terms, but a flow model which calls other expression definition to control execution flow of expressions:

IF IF expression_1 THEN expression_2

IFELSE IF expression_1 THEN expression_2 ELSE expression_3

DOWHILE DO expression_1 WHILE expression_2

WHILEDO WHILE expression_1 DO expression_2