Although KEKS can be decoded without any schema definition/specification,
data structures are likely to be checked against some kind of the schema.
Here is suggestion (not a requirement!) to use relatively simple data
structure validation specifications/schemas.

How are data structures checked? You check if they have required fields,
have necessary types of fields, satisfying lengths of the lists/maps or
strings, and so on. In most cases those checks covers nearly everything
when you sanitise the structures.

So suggestion is to specify those steps for some kind of the
interpreter, that executes validation commands ([schema/cmds]) against
the provided data structures. That interpreter should be simple enough
to be able to implement it quickly and with sane amount of code.
Validation steps should be easily decodable and conveniently parsed even
in C-language.

Let's use KEKS format itself for the serialised validation steps! And
generate them from higher level language/code ([schema/tcl]), convenient
for humans.

    [schema/tcl] -> [schema/cmds] -> keks-encode() => schema
    validate(schema, data)
