I am trying to make a Lua filter that will replace the normal link text in internal links with section numbers. I want to use internal links in my markdown document like this:

So, the links are given by the full title of the respective section they refer to. I found a recipe at stackoverflow (https://stackoverflow.com/questions/54128461/how-to-use-latex-section-numbers-in-pandoc-cross-reference) which does this if the link is given like this:

local make_sections = (require 'pandoc.utils').make_sections
local section_numbers = {}

function populate_section_numbers (doc)
function populate (elements)
for _, el in pairs(elements) do
if el.t == 'Div' and el.attributes.number then
section_numbers['#' .. el.attr.identifier] = el.attributes.number
populate(el.content)
end
end
end
populate(make_sections(true, nil, doc.blocks))
end

function resolve_section_ref (link)
if #link.content > 0 or link.target:sub(1, 1) ~= '#' then
return nil
end
local section_number = pandoc.Str(section_numbers[link.target])
return pandoc.Link({section_number}, link.target, link.title, link.attr)
end

return {
{Pandoc = populate_section_numbers},
{Link = resolve_section_ref}
}

While I do understand what it does, I cannot find out how to change it to my case. How can I retrieve the part written in [] instead of the attributes when scanning the document for those internal links? Or is the not even possible?