is json predicate

https://modern-sql.com/caniuse/is-json

IS JSON is a predicate to determine if the previous is a JSON object.

The SQL 2016 syntax is (2:8.22)

<expr> [ FORMAT JSON [ ENCODING { UTF8 | UTF16 | UTF32 } ] ]

       IS [ NOT ] JSON

       [ { VALUE | ARRAY | OBJECT | SCALAR } ]

       [ { WITH | WITHOUT } UNIQUE [ KEYS ] ]

but can only implement a subset of it, of course.

With IS being a parsed comparison its a small extension.