This will probably require an erratum. On 2023-06-13 we applied errata to the DFDL spec, and one of these errata fixes is actually incorrect. The correction says: Section 18.5.1 the xs:dateTime function takes 2 arguments, an xs:date and xs:time. This is not consistent with the XPath constructor function of that name, which takes a single argument: - xs:dateTime($arg as xs:anyAtomicType?) as xs:dateTime? DFDL spec also describes an fn:dateTime function - same signature - two arguments, in that same section (table 57). This is correct and consistent with XPath. Mike Beckerle Apache Daffodil PMC | daffodil.apache.org OGF DFDL Workgroup Co-Chair | www.ogf.org/ogf/doku.php/standards/dfdl/dfdl Owl Cyber Defense | www.owlcyberdefense.com