So, self-delimitered format (JSON) is embedded in format with lengths? I change one space in JSON, JSOM is valid, whole DiffX file is invalid.

Nice, nice.

Format looks very clunky and messy, to be honest, mixture of self-invented headers and JSON payloads, strange structure (without comments here I will not notice different number of dots in `.meta`), need essentialy two parsers.

Idea to have extended diff with standard way to put metadata is good.

This implementation looks bad, sorry.