[1] XPath and XQuery Functions and Operators 3.1 ( 版) <http://www.w3.org/TR/xpath-functions-3/#rules-for-datetime-formatting>
[2] XPath and XQuery Functions and Operators 3.1 () <https://www.w3.org/TR/2017/REC-xpath-functions-31-20170321/#syntax-of-picture-string>
[3] XPath and XQuery Functions and Operators 3.1 () <https://www.w3.org/TR/2017/REC-xpath-functions-31-20170321/#date-picture-string>
[4] XSL Transformations (XSLT) Version 3.0 () <https://www.w3.org/TR/2017/REC-xslt-30-20170608/#dt-picture-string>