Markdown post processing

Developers: Plugin & API
1
  1. How do I make registerMarkdownPostProcessor process all open notes? It seems to process only the first opened note when the plugin is loaded, and then does nothing.
  2. When called, I can use .appendChild to add any element to the currently processed element, but I can’t use it on the element’s parent div (‘markdown-preview-sizer markdown-preview-section’) to add a new element at the bottom (calling .appendChild does nothing in this case). Why is that?