Hello all,

I recently wrote a paper called "Capabilites and Class Extensions for
Secure but Extensible, Shared Smalltalk".  It discusses securing classes
in a shared environment while still allowing benign class extensions. 
It allows different packages to extend classes without changing them or
overriding them.  It is not as flexible as my layered environments
approach that I have previously proposed recently, but is more secure. 
I think it achieves a good compromise between extensibility and security
and should be considered for Croquet.  Check it out at:

http://minnow.cc.gatech.edu/squeak/SharedSmalltalk

Cheers,
Anthony