* 値 [CODE(JS)@en[NaN]] (JavaScript)

[1]
>The [[primitive value]] [DF[[CODE(JS)@en[NaN]]]] represents the [[set]] of [[IEEE Standard]] 
"[[Not-a-Number]]" [[values]]. This [[value]] is a [[member]] of the [CODE(JS)@en[[[Number]]]] [[type]].

;; [CITE[ECMAScript Language Specification (HTML version)]] ([TIME[2009-04-03 04:43:48 +09:00]] 版) <http://bclary.com/2004/11/07/#a-4.3.23>

[2]
:名前:[CODE(JS)@en[[[NaN]]]]
:型:[CODE(JS)@en[[[Number]]]]


[3] [CITE@EN[XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition)]]
( ([TIME[2010-12-17 00:06:54 +09:00]] 版))
<http://www.w3.org/TR/2010/REC-xpath-functions-20101214/#numeric-types>

* [CODE[nan]], [CODE[-nan]] (Perl)

[4] 
[PRE(perl code)[
$ perl -MPOSIX -MDevel::Peek -e 'print Devel::Peek::Dump POSIX::fmod(12,0)'
SV = NV(0x1c3cca8) at 0x1c2c780
  REFCNT = 1
  FLAGS = (PADTMP,NOK,pNOK)
  NV = -nan
]PRE]