So far EOF validation implementations return their own error code it is rather difficult to match them one-to-one.

Here is an idea to extend the return type to a tuple:

• error code (8 bits) (as it is now)
• error category (8 bits)
• element index (32 bits?)

The error category is "more standardized" way of informing at what phase of validation the error happened. E.g. header, body, type section, code section, subcontainer.

The index informs at which element the error happened. We need to find a global or category-based recursive indexing.
First of all, we need to find a convenient method of numbering all subcontainers.