Investigate a TODO with invalid mapping

DEVSIX-6676

Author: AnhelinaM

layout/src/test/java/com/itextpdf/layout/LayoutTaggingPdf2Test.java

@@ -391,14 +391,16 @@ public void docWithInvalidMapping03() throws IOException {
 
     @Test
     public void docWithInvalidMapping04() throws IOException, InterruptedException, ParserConfigurationException, SAXException {
-        // TODO this test passes, however it seems, that mingling two standard namespaces in the same tag structure tree should be illegal
-        // May be this should be checked if we would implement conforming PDF/UA docs generations in a way PDF/A docs are generated
         PdfDocument pdfDocument = new PdfDocument(new PdfWriter(destinationFolder + "docWithInvalidMapping04.pdf",
                 new WriterProperties().setPdfVersion(PdfVersion.PDF_2_0)));
         pdfDocument.setTagged();
 
         TagStructureContext tagsCntxt = pdfDocument.getTagStructureContext();
         PdfNamespace stdNs2 = tagsCntxt.fetchNamespace(StandardNamespaces.PDF_2_0);
+        // For /P elem a namespace is not explicitly specified, so PDF 1.7 namespace is used (see 14.8.6.1 of ISO 32000-2).
+        // Mingling two standard namespaces in the same tag structure tree is valid in "core" PDF 2.0, however,
+        // specifically the interaction between them will be addressed by ISO/TS 32005, which is currently still being drafted
+        // (see DEVSIX-6676)
         stdNs2.addNamespaceRoleMapping(HtmlRoles.p, StandardRoles.P);