I did something with JSON back before there was reasonable native support - it's certainly not robust, but it handled a few syntax variants for a use case where we had an extra attribute column that serialized JSON, and wanted to surface one of the fields as a proper column on the table.
https://blog.tracefunc.com/2011/11/19/parsing-json-in-sql-ht...
Funnily, I’m actively working on rewriting a stored procedure which parses an XML snippet as one of its arguments
Luckily it’s not a handwritten XML parser though: https://learn.microsoft.com/en-us/sql/t-sql/functions/openxm...
Just around the same time I was working at a place that used Oracle's web app extension, with CGI endpoints written completely in PL/SQL. I did end up writing an XML parser/serializer for it.
IMO, this kind of thing is what AoC is good for - you get to play with weird/obscure stuff without affecting your day job code.