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S-Expressions are missing. Language support is poor (except if you're programming in a Lisp dialect in which case it's built-in), but I do believe they are the best serialization format out there:

http://wiki.c2.com/?XmlIsaPoorCopyOfEssExpressions

They have a canonical representation

https://en.wikipedia.org/wiki/Canonical_S-expressions

I swear I have seen a proposal for an efficient binary representation somewhere but I can't find it.

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As far as I understand S-expressions are completely code-as-data, so how do you protect yourself from malicious code execution when loading S-expressions?

Simply not passing any of these parsed expressions to your eval function.

ANSI Common Lisp presents a pitfall here in that it features read-time evaluation via the #. (hash dot) syntax. For instance #.(+ 2 2) produces the object 4. After seeing #., he reader scans the (+ 2 2) expression, evaluates it immediately, and substitutes the result. When reading untrusted data in Common Lisp, the * read-eval * variable must be set to nil to disable hash-dot.

Lisps that don't have a read-time-eval escape mechanism don't require anything.

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