Chapter 19 describes the new interp command and the Safe-Tcl security mechanism. You can create multiple Tcl interpreters in your application and control them with the interp command. You create command aliases so that the interpreters can exchange Tcl commands. If an interpreter is created in a safe mode, then its set of Tcl commands is restricted so that its scripts cannot harm your computer or application. However, with aliases you can give the untrusted scripts limited access to resources.