On top of demo.tcl script place:
package require Tcl 8.6
Emulations and improvements:
package: added provide, names, vsatisfies.
package require demo .. also searches in demo subdirectory of each auto_path element.interp: added create, issafe, alias.encoding: added names.socket: reduce to work with stream only and use original syntax.fconfigure: add some options.fcopyinfo: added args, default, errorstack.