How can I create a Lua filter that changes italic & bold markdown to Emphasis & Strong Emphasis styles with pandoc for LibreOffice Writer ODT file?

I have input.md:

---
title: My example document
---

## Overview

*I am italic*

**I am bold**

If I run:

pandoc input.md -o output.odt

I get an odt file with the expected formatting. However, in order to prepare the document for conversion to a PDF/UA-compliant PDF, I have to manually remove the bold and italic formatting and style those text items as "Strong Emphasis" and "Emphasis", respectively, from the Styles menu.

I want to automate this, so I created custom_styles.lua:

function Strong(elem)
    return pandoc.Span(elem.content, {class = "StrongEmphasis"})
end

function Emph(elem)
    return pandoc.Span(elem.content, {class = "Emphasis"})
end

If I run:

pandoc --lua-filter=custom_styles.lua -o output.odt input.md

My odt document now shows "No Character Style" for the text that was bold and italic.

Can somebody explain what I should be doing to achieve this?

Thanks I

Solution

This should work, but the custom styles must already exist in the reference odt.

To create the reference ODT, first run

pandoc --output=my-refdoc.odt --print-default-data-file=reference.odt

Edit the resulting file my-refdoc.odt, add the custom styles, and then pass the modified file to pandoc via --reference-doc=my-refdoc.odt when doint the conversion.

The filter should set the custom-style attribute, so the code should use {['custom-style'] = "StrongEmphasis"}.

Everything should work once those things are in place.