https://manpages.ubuntu.com/manpages/xenial/man3/Tcl_UnsetVar.3tcl.html
Ubuntu Manpage: Tcl_SetVar2Ex, Tcl_SetVar, Tcl_SetVar2, Tcl_ObjSetVar2,
ubuntumanpagetclsetvar
https://manpages.ubuntu.com/manpages/xenial/man3/Tcl_ObjSetVar2.3tcl.html
Ubuntu Manpage: Tcl_SetVar2Ex, Tcl_SetVar, Tcl_SetVar2, Tcl_ObjSetVar2,
ubuntumanpagetclsetvar
https://manpages.ubuntu.com/manpages/xenial/man3/Tcl_SetVar.3tcl.html
Ubuntu Manpage: Tcl_SetVar2Ex, Tcl_SetVar, Tcl_SetVar2, Tcl_ObjSetVar2,
ubuntumanpagetclsetvar
https://manpages.ubuntu.com/manpages/xenial/man3/Tcl_GetVar2.3tcl.html
Ubuntu Manpage: Tcl_SetVar2Ex, Tcl_SetVar, Tcl_SetVar2, Tcl_ObjSetVar2,
ubuntumanpagetclsetvar
https://manpages.ubuntu.com/manpages/xenial/man3/Tcl_UnsetVar2.3tcl.html
Ubuntu Manpage: Tcl_SetVar2Ex, Tcl_SetVar, Tcl_SetVar2, Tcl_ObjSetVar2,
ubuntumanpagetclsetvar