add version test

required/latex-lab/latex-lab-math.dtx

@@ -1165,8 +1165,13 @@
 \bool_gset_true:N \g_@@_luamml_write_bool
 %    \end{macrocode}
 % \end{variable}
-
+%
 %    \begin{macrocode}
+\msg_new:nnn { tag }{ PDF-2.0-recommended }
+  {
+    The~key~#1~will~not~work~properly~with~PDF~#2.\\
+    Switching~to~PDF~2.0~is~recommended.
+  }
 \keys_define:nn { __tag / setup }
    {
 %    \end{macrocode}
@@ -1182,7 +1187,14 @@
 % be issued in the preamble as luamml is not yet loaded.
 %    \begin{macrocode}
      math/mathml/structelem .code:n =
-      {\AddToHook{begindocument/end}{\luamml_structelem:}},
+      {
+        \pdf_version_compare:NnT < {2.0}
+         {
+          \msg_warning:nnne { tag }{ PDF-2.0-recommended }
+           { math/mathml/structelem }{ \pdf_version: }
+         }
+        \AddToHook{begindocument/end}{\luamml_structelem:}
+      },
 %    \end{macrocode}
 % and a key to call the ignore flag. This should only be used locally.
 %    \begin{macrocode}