M11: PDF/A verify allows only XMP's value forms: one rdf:value, parseType Resource, empty rdf:resource (6.6.2.3.1)

A qualified value has exactly one rdf:value; a parse type other than
Resource, which XMP doesn't use (ISO 16684-1 7.9.2.5), breaks the value;
and an rdf:resource element holds no element content in any form.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyDBXygTf7jcqdsjcfn

crates/preflight/src/tests.rs

@@ -708,3 +708,21 @@ fn xmp_value_types_are_reported_by_verify() {
     );
     assert_eq!(issues(&doc).len(), 1);
 }
+
+/// PDF/A-2 6.6.2.3.1, the RDF/XML value forms XMP allows (ISO 16684-1 7.9.2.5): one `rdf:value`
+/// in a qualified value, no parse type but `Resource`, and an `rdf:resource` element left empty.
+#[test]
+fn xmp_value_forms_are_those_xmp_allows() {
+    // A qualified value has exactly one rdf:value.
+    assert_eq!(
+        mistyped(r#"><crs:Contrast rdf:parseType="Resource"><rdf:value>5</rdf:value><rdf:value>five</rdf:value></crs:Contrast>"#),
+        ["crs:Contrast"]
+    );
+    // Only parseType="Resource" has a place in XMP; an rdf:resource element holds no element.
+    assert_eq!(mistyped(r#"><crs:Contrast rdf:parseType="Literal">5</crs:Contrast>"#), ["crs:Contrast"]);
+    assert_eq!(mistyped(r#"><xmpMM:DerivedFrom rdf:parseType="Literal" stRef:documentID="d"/>"#), ["xmpMM:DerivedFrom"]);
+    assert_eq!(
+        mistyped(r#"><xmpMM:DerivedFrom rdf:resource="urn:example"><rdf:Description stRef:documentID="d"/></xmpMM:DerivedFrom>"#),
+        ["xmpMM:DerivedFrom"]
+    );
+}

crates/preflight/src/xmp_types.rs

@@ -535,6 +535,11 @@ fn fits(ty: Ty, e: &Node<'_, '_>, depth: usize) -> bool {
     let children: Vec<Node<'_, '_>> = e.children().filter(Node::is_element).collect();
     // A qualified value: `rdf:value` holds the value itself (ISO 16684-1 7.9.2.5).
     let resource = e.attribute((RDF, "parseType")) == Some("Resource");
+    // `parseType="Resource"` is the only parse type XMP has (ISO 16684-1 7.9.2.5); an
+    // `rdf:resource` element is empty.
+    if e.attribute((RDF, "parseType")).is_some_and(|p| p != "Resource") || e.attribute((RDF, "resource")).is_some() && !children.is_empty() {
+        return false;
+    }
     let description = match children.as_slice() {
         [d] if is(d, RDF, "Description") => Some(*d),
         _ => None,
@@ -543,10 +548,13 @@ fn fits(ty: Ty, e: &Node<'_, '_>, depth: usize) -> bool {
     // attribute of the description or of an empty property element. Its qualifiers that are
     // predefined properties keep their types too.
     let node = if resource { Some(*e) } else { description };
-    if let Some(n) = node
-        && let Some(v) = n.children().find(|c| is(c, RDF, "value"))
-    {
-        return blank(e) && blank(&n) && fits(ty, &v, deeper) && predefined_ok(&n, deeper);
+    if let Some(n) = node {
+        // A qualified value has one `rdf:value`.
+        match n.children().filter(|c| is(c, RDF, "value")).collect::<Vec<_>>().as_slice() {
+            [] => {}
+            [v] => return blank(e) && blank(&n) && fits(ty, v, deeper) && predefined_ok(&n, deeper),
+            _ => return false,
+        }
     }
     let attribute_node = description.or_else(|| (children.is_empty() && !resource).then_some(*e));
     if let Some(n) = attribute_node