clarity needed for the non-sealed keyword

[Brian Goetz]

> But why does the keyword contain a “-”?  Why wasn't “nonsealed” good
> enough?

The rationale for the creation of hyphenated keywords is well 
documented.  See, for example:

http://mail.openjdk.java.net/pipermail/amber-spec-experts/2019-January/000945.html

and

https://openjdk.java.net/jeps/8223002