reference marks in text/html clipboard

I am working on a web application (Fidus Writer) that work on the clipboard output that comes out of LibreOffice Writer. That works quite well for most content, but there is one exception: For some reason reference-mark-* tags are just entirely removed when the HTML is formed. Why is that? Reference managers like Zotero store valuable information in those tags so it would be great to handle those in the HTML. Can anyone point me to where the serialization to html for clipboard takes place in the sources?

Please, does anyone can help on this?
Thank you.