Pandoc Lua Filter: How to access the title variable?

Question

My document looks like this

---
title: 'Test'
---

lorem ipsum

I want to access the title variable to print it like this:

function Image (elem)
elem.attributes.caption = 'Image of chapter ' .. title
return elem

The caption of all images should be: 'Image of chapter Test'.

Answer 1

Something like this should work (untested), inspired by the docs:

title = nil

function Meta(m)
  title = m.title
  return m
end

function Image (elem)
  elem.attributes.caption = 'Image of chapter ' .. title
  return elem
end