doc: Update the template to render sub-tags.

Sub-tags are a new concept and is equivalent to @tparam, but in
a generic form.

docs/ldoc.ltp

@@ -204,21 +204,6 @@
     <dd>
     $(M(ldoc.descript(item),item))
 
-#   if ldoc.custom_tags then
-#    for custom in iter(ldoc.custom_tags) do
-#     local tag = item.tags[custom[1]]
-#     if tag and not custom.hidden then
-#      local li,il = use_li(tag)
-    <h3>$(custom.title or custom[1]):</h3>
-    <ul>
-#      for value in iter(tag) do
-         $(li)$(custom.format and custom.format(value) or M(value))$(il)
-#      end -- for
-#     end -- if tag
-    </ul>
-#    end -- iter tags
-#   end
-
 #  if show_parms and item.params and #item.params > 0 and not item.hide_params then
 #    local subnames = module.kinds:type_of(item).subnames
 #    if subnames then
@@ -307,6 +292,36 @@
     </ul>
 #   end -- if usage
 
+#   if ldoc.custom_tags then
+#    for custom in iter(ldoc.custom_tags) do
+#     local tag = item.tags[custom[1]]
+#     if tag and not custom.hidden then
+#      local group_begin, group_end, row_type_begin, row_type_end, group_header = item.get_delim(custom[1])
+    <h3>$(custom.title or custom[1]):</h3>
+    <$(group_begin)>
+#      if group_header then
+        <tr style='font-weight: bold;'>
+#       for _, g in ldoc.ipairs(group_header) do
+          <th>$(g)</th>
+#       end -- for g
+        </tr>
+#      end -- if group_header then
+#      for value in iter(tag) do
+         <$(row_type_begin)>$(custom.format and custom.format(value, item, M) or M(value))</$(row_type_end)>
+#        local sub_values, sub_custom = item.get_auto_params(custom[1], value)
+#        if sub_values then
+          <ul>
+#         for _, value in ldoc.ipairs(sub_values) do
+            <li>$(sub_custom.format(value, item, M))</li>
+#         end -- for auto_params
+          </ul>
+#        end -- if item.auto_params
+#      end -- for
+    </$(group_end)>
+#     end -- if tag
+#    end -- iter tags
+#   end -- ldoc.custom_tags
+
 </dd>
 # end -- for items
 #  last_kind = kind