Shared.hierarchicalize: improve handling of div and section structure.

Previously Divs were opaque to hierarchicalize, so headings
inside divs didn't get into the table of contents, for
example (#3057).

Now hierarchicalize treats Divs as sections when appropriate.
For example, these structures both yield a section and a
subsection:

``` html
<div>
<h1>one</h1>
<div>
<h2>two</h2>
</div>
</div>
```
``` html
<div>
<h1>one</h1>
<div>
<h1>two</h1>
</div>
</div>
```

Note that

``` html
<h1>one</h1>
<div>
<h2>two</h2>
</div>
<h1>three</h1>
```

gets parsed as the structure

    one
      two
    three

which may not always be desirable.

Closes #3057.

1 files changed, 54 insertions, 0 deletions

diff --git a/test/command/3057.md b/test/command/3057.md
new file mode 100644
index 000000000..b1f3a8c2e
--- /dev/null
+++ b/test/command/3057.md
@@ -0,0 +1,54 @@
+```
+% pandoc -f markdown -t docbook
+<div>
+# one
+<div>
+## two
+</div>
+</div>
+^D
+<section>
+  <title>one</title>
+  <section>
+    <title>two</title>
+    <para>
+    </para>
+  </section>
+</section>
+```
+
+```
+% pandoc -f markdown -t docbook
+<div>
+# one
+<div>
+# two
+</div>
+</div>
+^D
+<section>
+  <title>one</title>
+  <section>
+    <title>two</title>
+    <para>
+    </para>
+  </section>
+</section>
+```
+
+```
+% pandoc -f markdown -t docbook
+# one
+<div>
+# two
+</div>
+^D
+<section xml:id="one">
+  <title>one</title>
+  <section>
+    <title>two</title>
+    <para>
+    </para>
+  </section>
+</section>
+```