fn:number

fn:number() as xs:double

fn:number($arg as xs:anyAtomicType?) as xs:double

The zero-argument form of this function is deterministic, context-dependent, and focus-dependent.

The one-argument form of this function is deterministic, context-independent, and focus-independent.

Calling the zero-argument version of the function is defined to give the same result as calling the single-argument version with the context item (.). That is, fn:number() is equivalent to fn:number(.), as defined by the rules that follow.

If $arg is the empty sequence or if $arg cannot be converted to an xs:double, the xs:double value NaN is returned.

Otherwise, $arg is converted to an xs:double following the rules of Casting to xs:double. If the conversion to xs:double fails, the xs:double value NaN is returned.

A dynamic error is raised [ERRXPDY0002] if $arg is omitted and the context item is absent.

As a consequence of the rules given above, a type error occurs if the context item cannot be atomized, or if the result of atomizing the context item is a sequence containing more than one atomic value.

XSD 1.1 allows the string +INF as a representation of positive infinity; XSD 1.0 does not. It is implementation-defined whether XSD 1.1 is supported.

Generally fn:number returns NaN rather than raising a dynamic error if the argument cannot be converted to xs:double. However, a type error is raised in the usual way if the supplied argument cannot be atomized or if the result of atomization does not match the required argument type.

The expression fn:number($item1/quantity) returns 5.0e0.

The expression fn:number($item2/description) returns xs:double('NaN').

Assume that the context item is the xs:string value "15". Then fn:number() returns 1.5e1.