There are some debates about declining use of XML and rising use of JSON. Some people love XML, some people love JSON. I love SAX: assuming SAX serializer/deserializers exist, anything can be treated as XML.
For example, you can write XSLT stylesheets transforming JSON: JSON SAX deserializer was already created by me in my previous article "How to Convert JSON to XML using ANTLR" and JSON SAX serializer is fairly easy to write. Once you have all that, you can transform JSON using XSLT:
In the previous article I have shown how to convert JSON to XML using XSLT 2.0 capabilities.
The problem w/ implementing parsers in XSLT, is conversion from flat structure to tree structure. XSLT was simply NOT created for such kind of conversions. For example, JSON to XML transformation is using XML Pipeline of mode1, mode2, mode3 to build a tree structure from a sequence of tokens generated by regexp in mode0.