Work around lack of `datetime-local` input support in 2019

example-puzzles/example/5/helpers.js

@@ -17,7 +17,11 @@ function helperUpdateAnswer(event) {
         values.push(c.value)
       }
     }
-    value = values.join(",")
+    let join = e.dataset.join
+    if (join === undefined) {
+      join = ","
+    }
+    value = values.join(join)
   }
 
   // First make any adjustments to the value

example-puzzles/example/5/puzzle.moth

@@ -17,8 +17,13 @@ This is just a demonstration page.
 You will probably only want one of these in a page,
 to avoid confusing people.
 
-Timestamp
-<input type="datetime-local" class="answer">
+RFC3339 Timestamp
+<div class="answer" data-join="">
+  <input type="date">
+  <input type="hidden" value="T">
+  <input type="time" step="1">
+  <input type="hidden" value="Z">
+</div>
 
 All lower-case letters
 <input class="answer lower">