* We reject leading underscores in bareword.  No sensible reason why.
     * Might be inspired by reserved identifier rules in C, which of course
     * have no direct relevance here.
     */

    if (!TclIsBareword(*start) || *start == '_') {
	if (Tcl_UtfCharComplete(start, numBytes)) {
	    scanned = Tcl_UtfToUniChar(start, &ch);
	} else {
	    char utfBytes[TCL_UTF_MAX];

	    memcpy(utfBytes, start, (size_t) numBytes);
	    utfBytes[numBytes] = '\0';
	    scanned = Tcl_UtfToUniChar(utfBytes, &ch);
	}
	*lexemePtr = INVALID;
	Tcl_DecrRefCount(literal);
	return scanned;
    }
    end = start;
    while (numBytes && TclIsBareword(*end)) {