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Slave interpreters are Tcl interpreters that are children of some other interpreter (called the master). They are used in cases where there is a need to evaluate a Tcl script in a context that is substantially different from that of the main Tcl program, such as
Processing untrusted code
Handling a plugin mechanism for a larger program that does not expose the details of the main body of the application
Creating a friendlier API for configuring an application
Isolating executions of some code from each other
Limiting the resources that may be used for a particular operation