RFC5322?

* No more "allowable ranges", you can have any range of Unicode
characters you feel you can handle, and on your own head be it
* Greenery can now parse characters given as hex escapes e.g. you can
input "\\x00" instead of a literal null
* ASCII control characters are likewise output as hex (this is a little
inelegant at the moment due to magic numbers)
* Explicitly non-capturing group "(?: ... )" is supported (but does
nothing, since greenery has never supported capture groups anyway)
* Unit tests