sub search_text {

    # The utility procedure below searches for all instances of a given
    # string in a text widget and applies a given tag to each instance found.
    # Arguments:
    #
    # w -	The window in which to search.  Must be a text widget.
    # string -	Reference to the string to search for.  The search is done
    #           using exact matching only;  no special characters.
    # tag -	Tag to apply to each instance of a matching string.
    # kind    rexexp or exact

    my($w, $string, $tag, $kind) = @_;

    return unless ref($string) && length($$string);

    $w->tagRemove($tag, qw/0.0 end/);
    my($current, $length) = ('1.0', 0);

    while (1) {
	$current = $w->search(-count => \$length, "-$kind", $$string, $current, 'end');
	last if not $current;
	warn "Posn=$current count=$length\n",
	$w->tagAdd($tag, $current, "$current + $length char");
	$current = $w->index("$current + $length char");
    }

} # end search_text