These expressions are used to display data, to construct queries, to sort data, to enter and edit data, and to conditionally display data.
Expressions return a value of a specific type.
Expressions used to display data must return a character value. Expressions used to enter or edit data must return the same type as the field. Expressions used to query data or for conditional display must return a logical value. Expressions used to sort data in an index expression may be any type except logical. Expressions consist of constants, operators, field values, and functions.