require("helpview").setup({
 renderers = {
 --- Custom renderer for YAML properties.
 ---@param ns integer Namespace to use for extmarks.
 ---@param buffer integer Buffer where 
 ---@param item vimdoc.__code_block The parsed version of a node.
 vimdoc_code_block = function (ns, buffer, item)
 --- Do custom stuff.
 end
 }
})

The structure and data of an item can be found in their option's wiki section. For example, to see the one for vimdoc_heading head over to Vimdoc options.md in the wiki and go to the headings section. You will find the definition of item inside the drop-down.

Currently supported items are,

• vimdoc

  • vimdoc_argument
  • vimdoc_code_block
  • vimdoc_heading
  • vimdoc_hl (highlight group name)
  • vimdoc_hr (horizontal rules)
  • vimdoc_inline_code
  • vimdoc_keycode
  • vimdoc_modeline
  • vimdoc_note
  • vimdoc_optionlink
  • vimdoc_tag
  • vimdoc_taglink
  • vimdoc_url

Also available in vimdoc, :h helpview.nvim-renderers