[1] XPath and XQuery Functions and Operators 3.1 (2014-12-18 06:45:18 +09:00 版) http://www.w3.org/TR/xpath-functions-3/#rules-for-datetime-formatting

[2] XPath and XQuery Functions and Operators 3.1 (2017-03-21 16:02:06 +09:00) https://www.w3.org/TR/2017/REC-xpath-functions-31-20170321/#syntax-of-picture-string

[3] XPath and XQuery Functions and Operators 3.1 (2017-03-21 16:02:06 +09:00) https://www.w3.org/TR/2017/REC-xpath-functions-31-20170321/#date-picture-string

[4] XSL Transformations (XSLT) Version 3.0 (2017-06-06 21:59:56 +09:00) https://www.w3.org/TR/2017/REC-xslt-30-20170608/#dt-picture-string