walk!(x::Any, action::Function, format, meta)

Walk the Pandoc document abstract source tree (AST) and apply filter function on each element of the document AST, modifying the tree in place.

• action must be a function which takes four arguments, tag, content, format, meta, and should return:
  • nothing to leave the element unchanged
  • [] to delete the element
  • A Pandoc element to replace the element
  • or a list of Pandoc elements which will be spliced into the list the original object belongs to.