> Sorry not a good example

I just pulled the example from the article ‘Designing Extensible, Versionable XML Formats’ hosted at xml.com. Presumably xml.com has decent examples of XML?

I an pretty sure that author is not a singular data type, since it is possible for a book to have multiple authors.

> Sweet, succinct, elegant

I think it’s still inelegant in comparison to the S-expression version.

> The above can be parsed without bugginess or insecurity - those feel like opinions to me.

A quick Googling for ‘xml parsing cve’ shows plenty of hits. Are you familiar with billion-laughs exploits? XML is well-known for them: https://en.wikipedia.org/wiki/Billion_laughs_attack