this test file just exists to reproduce a bug with footnotes in headlines - that only happens in very specific circumstances. The TLDR is:

• HTMLWriter.footnotes should be a pointer field. I didn't notice my error as go translated my pointer-method calls on non-pointer values rather than complaining - i.e. footnotes.add() transparently gets translated to (&footnotes).add() (docs).

• Headlines have to be htmlified twice - once for the outline and once for the headline itself. To do so we have to copy the writer

• Copying the writer copies footnotes - which contains a map and a slice. Changes to the map will always be reflected in the original map. Changes to the slice will only be reflected if the slice doesn't grow.

• We can thus end up with a footnote being in the mapping but not the slice - and get an index out of range error.