JSON is not extensible and syntactically more verbose. However, the syntax corresponds exactly to many modern dynamic languages and is now nearly ubiquitous.

> Of course JSON (http://www.ietf.org/rfc/rfc4627.txt) does this as well but using character code points.

I hope Rich will define "alphanumeric" as Unicode letter and number classes. Clojure itself is ambiguous on valid symbol identifiers. http://clojure.org/reader has the same "alphanumeric plus some punctuation" rule, but the actual reader implementation [1] is extremely permissive:

    static Pattern symbolPat = Pattern.compile("[:]?([\\D&&[^/]].*/)?([\\D&&[^/]][^/]*)");

[1]: https://github.com/clojure/clojure/blob/master/src/jvm/cloju...