Returns the value indicated by $arg or, if $arg is not
specified, the context item after atomization, converted to an xs:double.
fn:number( xs:doublefn:number( $arg as xs:anyAtomicType?xs:doubleCalling 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, $arg is converted to an xs:double following the
rules of . If the conversion to xs:double
fails, the xs:double value NaN is returned.
The expression fn:number($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.
A dynamic error is raised
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.
