Fix makeSections so it doesn't turn column divs into sections.

src/Text/Pandoc/Shared.hs

@@ -586,7 +586,9 @@ makeSections numbering mbBaseLevel bs =
        (Header level (ident,classes,kvs) title':ys) : xs)
       | all (\case
                Header level' _ _ -> level' > level
-               _                 -> True) ys = do
+               _                 -> True) ys
+      , "column" `notElem` dclasses
+      , "columns" `notElem` dclasses = do
     inner <- go (Header level (ident,classes,kvs) title':ys)
     let inner' =
           case inner of

test/command/make-section-column-divs.md

@@ -0,0 +1,28 @@
+For reference see
+https://groups.google.com/d/msgid/pandoc-discuss/cef24253-7731-417c-a1ee-48153c4344bf%40googlegroups.com
+
+```
+% pandoc
+::: columns
+::: column
+# A
+
+a
+:::
+::: column
+# B
+
+b
+:::
+:::
+^D
+<div class="columns">
+<div class="column">
+<h1 id="a">A</h1>
+<p>a</p>
+</div><div class="column">
+<h1 id="b">B</h1>
+<p>b</p>
+</div>
+</div>
+```