The MobileFormatter:prepareHeadings method is over-zealous about which headings are collapsible. This could be leading to various edge cases where headings work inappropriately resulting in strange UI's being exposed to our readers.
= Suggested implementation
As @TheDj suggests this could be remedied by a refactor of MobileFormatter::makeSections.
[] Repurpose prepareHeadings to prepareHeading
[] Before inserting sectionBody a call to prepareHeading should be run on the $node (the heading)
= Acceptance Criteria
[] Add a test to capture the example in https://en.m.wikipedia.beta.wmflabs.org/wiki/Headings_in_infobox - expected behaviour is that the heading inside the infobox should not have 'section-heading' class or an onlick event.
[] In certain cases no headings should be transformed, for example any headings inside a div e.g. "Off the beaten path" in [[ https://en.m.wikivoyage.org/w/index.php?title=User:Jdlrobson/main_page | this example ]] should be left untouched.
```
Headings_in_infobox:60 Uncaught TypeError: Cannot read property 'className' of null(…)
```