Subcommand of wm to query or set the title of a toplevel window. For editor-like apps, it is convenient to put the current file name into the title bar:
wm title $w $filename
or, combined with the app name (Windows look & feel):
wm title $w "$filename - $appname"
You can even retrieve the filename from there with regexp, avoiding a global variable:
regexp "(.+) - $appname" [wm title $w] -> filename ;# RS