Version 5 of safe

http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/safe.htm

Safe Base - A mechanism for creating and manipulating safe interpreters.

Bob Techentin asked questions on comp.lang.tcl regarding the use of safe interpreters running code that uses the [package require] mechanism. The Safe Base supports some package loading, but is mentioned less often than [interp create -safe]

Bob Asked:

  How, in your opinion, Jacob, does [[::safe::interpCreate]] jibe with
  [[interp create -safe]]?  Am I foolish for wanting to grant something
  beyond core functionality to a safe interpreter?  If so, what is the
  real point of the Safe Base mechanism?

and Jacob Levy replied

  The answer is that nilly willy you're going to want to source some stuff 
  into a safe interpreter, open some scratch files etc. So, either you 
  come up with your own idiosyncratic solution, or use safe::interpCreate 
  to do it in a semi standard way.

  In other words, [interp create -safe] gives you a raw interpreter 
  without any aliases. That's of course also what safe::interpCreate does 
  internally. And then it adds some aliases that were very very carefully 
  designed to be safe (nearly as safe as the base safe interpreter that 
  [interp create -safe] returns. The Safe Base is therefore simply one way 
  to extend the raw safe interpreter, and has been carefully reviewed and 
  used extensively, so it's believed to be safe.

  If you were to roll your own, you could easily introduce some of the 
  bugs that the war tested Safe Base has already avoided.