All headings/panels within nested ol/ul lists get same parent accordion properties

[smillart]

First of all, great job!

The query selector you use for accordion headings/panels contained within an ol/ul list returns all descendant headings/panels in the main accordion (as well as the nested ones).

Currently:
panels = doc.querySelectorAll('#' + self.id + ' li > ' + widgetPanel);
headings = doc.querySelectorAll('#' + self.id + ' li > ' + widgetHeading);

Should be:
panels = doc.querySelectorAll('#' + self.id + ' > li > ' + widgetPanel);
headings = doc.querySelectorAll('#' + self.id + ' > li > ' + widgetHeading);