XSLT is very useful to transform nested structures. The input has to be XML, but you can get there via YAML, JSON, tree-sitter etc. And the output doesn't have

XSLT is very useful to transform nested structures. The input has to be XML, but you can get there via YAML, JSON, tree-sitter etc. And the output doesn't have to be XML. xsltproc is usually easy to install.