tcl_wordchars and tcl_nonwordchars are unknown at Tcl startup.

They are currently auto-loaded along with the commands they control (tcl_wordBreakAfter, tcl_wordBreakBefore, tcl_endOfWord, tcl_startOfNextWord, tcl_startOfPreviousWord). Only when one of these commands are used the file word.tcl where all this is defined is sourced.

That means that ::tcl_wordchars and ::tcl_nonwordchars cannot be used before using one of these commands first.

Therefore, running one of the following commands (for instance) make Tcl aware of tcl_wordchars and tcl_nonwordchars:
    catch {tcl_endOfWord}
    tcl_endOfWord "Hello world" 2  ; # or any parameters
    source [file join [info library] word.tcl]

But this should not be necessary from a user point of view: tcl_wordchars and tcl_nonwordchars should be readily available at Tcl session startup.

Note: this ticket is a follow-up from the following Tk ticket:
    http://core.tcl.tk/tk/tktview/1517768fffffffffffffffffffffffffffffffff

See also this comp.lang.tcl thread:
    http://groups.google.fr/group/comp.lang.tcl/browse_thread/thread/659fd6c1f41d9a81/4a3c30d2c97604cc

Another reference is in the wiki:
    http://wiki.tcl.tk/1655

tcl_wordchars and tcl_nonwordchars are unknown at startup