The Tcl::Tk submodule of the Tcl module gives access to the Tk library.  It does
this by creating a Tcl interpreter object (using the Tcl extension) and binding
in all of Tk into the interpreter (in the same way that wish or other Tcl/Tk
applications do).

Access to the Tcl and Tcl::Tk extensions

To get access to the Tcl and Tcl::Tk extensions, put the commands
    require Tcl;
    use Tcl::Tk;

near the top of your program. The Tcl extension does not alter your namespace at
all (hence the "require"). The Tcl::Tk extension imports the widget and other Tk
commands into your namespace (hence the "use").

WWW: http://search.cpan.org/dist/Tcl-Tk