Value types

Every attribute type is defined with an associated value type using the value keyword, which fixes the value that its attributes carry:

The same keyword retrieves attribute types by value type in a pattern, as in match $a value date;.

A literal written directly in a query is a constant of the value type determined by its syntax: 1 is an integer, 1.0 a double, true a boolean. Literals supply attribute values on insertion, operands in expressions and comparisons, arguments to function calls, and arguments to value constraints.

A variable assigned with let holds a computed value rather than a stored data instance. Its value type is inferred from the expression that produces it, and is checked when the query is compiled:

A function declares the type of each argument and each returned element. These may be value types as well as user-defined types:

Value types determine which comparisons are legal. Values may only be compared within a comparable group, and boolean and duration values compare for equality only.

The @values, @range, and @regex annotations take literal arguments that must match the value type of the attribute type they constrain. Each annotation supports a specific set of value types.