My experience is that LLMs are very good at using structure that is indicated by HTML tags, very good with structure that is indicated via Markdown, not so good with arbitrary XML tags that didn't appear much in their training corpus.
Care and feeding of LLMs: XML How Not To
My experience is that LLMs are very good at using structure that is indicated by HTML tags, very good with structure that is indicated via Markdown, not so good with arbitrary XML tags that didn't appear much in their training corpus.