local function words(s)
    local res = {}
    for part in s:gmatch("[^,]+") do                -- split by commas
        local trimmed = part:match("^%s*(.-)%s*$")  -- remove leading/trailing spaces
        if trimmed ~= "" then
            table.insert(res, trimmed)
        end
    end
    return res
end

local function label2Block(labels)
    local contents = ""
    for _,l in ipairs(words(labels)) do
        -- use file for now.
        local fh = io.open(l, "r")
        if not fh then
            io.stderr:write("Cannot open file: " .. l .. "\n")
            return { pandoc.Plain { pandoc.Str("[Error: cannot read file " .. l .. "]") } }
        end
        contents = contents .. fh:read("*a")
        fh:close()
    end
    return { pandoc.Plain { pandoc.Str(contents) } }
end

function Div(e)
    local include = e.attributes["include"]
    if include then
        local blocks = label2Block(include)
        -- Replace the Div contents
        return pandoc.Div(blocks, e.attr)
    end
    return nil -- no change
end