Expressions are combinations of variables or global properties and operators. The logic engine evaluates expressions primarily in order to determine what is displayed to the user as in applicability ([Model = "T"]) and branching ([If Error Condition = "4"]) and loop (WHILE [Counter < "5"]) conditions. Expressions are also used to assign a value to a variable or global property ([Ave = Sum / 3]). Refer to Chap 7.6.1.4 for detailed information.The element <expression> defines something to be evaluated by the logic engine. Expressions are used to assign values to variables in assertions, eg, the value of the expression [Counter plus 1] might be assigned to the variable Counter. They are also used in applicability, branches, and other constructs to determine what is displayed to the user. In element <applic>, for example, if the expression [Item deployed equal TRUE] evaluates to TRUE, the data item containing the applicability is displayed and vice versa. Expressions are authored by combining variables (or other expressions) and values with binary or unary operators. In their simplest form, an expression can be just a variable/global property or a value. The element <assert> can also be used to simplify the authoring of complicated expressions.