section ticking covers the section

plugins/guides/services/htmlimport.py

@@ -244,7 +244,12 @@ class _Builder:
         if tag in ('h2', 'h3', 'h4', 'h5'):
             text = _inline(node)
             if text:
-                self._add({'type': 'heading', 'text': text})
+                # The LEVEL travels with it. Without it every heading is a
+                # sibling, and a reader who ticks a section off crosses out its
+                # title and nothing underneath - the sub-headings that belong to
+                # it look untouched, because nothing recorded that they belong.
+                self._add({'type': 'heading', 'level': int(tag[1]),
+                           'text': text})
             return
 
         if tag == 'p':