Part VII describes the changes between versions of Tcl and Tk.
Chapter 48 has notes about porting your scripts to Tcl 7.4 and Tk 4.0. Chapter 49 describes changes in Tcl 7.5 and Tk 4.1. Chapter 50 describes changes in Tcl 7.6 and Tk 4.2. The Tcl and Tk version numbers were unified in the next release, Tcl/Tk 8.0, which is described in Chapter 51. New features added Tcl/Tk 8.1 are described in Chapter 52, and changes in Tcl/Tk 8.2 are described in Chapter 53.
Tcl/Tk 8.3 is in the planning stages as this book goes to press. An early view of these plans are presented in Chapter 54.