variant property
Variant picks a template's format/page/theme (optional; defaults to the template's first shape). This is the axis the catalog used to spend sibling slugs on, so it is expressed here, where the user's preference is.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? variant;