Creates a shape for ISO 8601 year values (YYYY).
Supports optional timezone indicators (Z for UTC or ±hh:mm offset).
Optional TextualConstraints validation constraints
A shape for validating ISO 8601 year strings
XSD permits timezone indicators for gYear as a deviation from ISO 8601.
XSD 1.1 Part 2: Datatypes § 3.3.11 gYear
Creates a shape for ISO 8601 year values (YYYY).
Supports optional timezone indicators (Z for UTC or ±hh:mm offset).