sub replace_split_1 {  # pre-5.10 safe: no // operator, no regex extensions

    my ($string,  # string to search/replace
        $srch,    # search string (no regex metacharacters)
        $repl,    # optional: replacement string (default: '')
        $n,       # optional: number of replacements (default: infinite)
        ) = @_;

    # handle degenerate cases.
    return ''      unless defined $string;
    return $string unless defined $srch && length $srch;  # ???

    # default replacement string: empty string.
    $repl = '' unless defined $repl;  # avoid // (defined-or) operator

    # replace right-to-left if n is defined and < 0.
    my $replace_right_to_left = defined($n) && $n < 0;

    # split limit: one more than absolute of replacement count
    # unless count is undefined/infinite.
    my $limit = defined $n ? 1+abs($n) : -1;  # split limit

    # reverse all strings if replacing right-to-left.
    if ($replace_right_to_left) {
        $_ = reverse for $string, $srch, $repl;
        }

    # split on meta-quoted search substring to specified limit.
    my @groups = split "\Q$srch", $string, $limit;

    # replace all instances of search substring.
    $string = join $repl, @groups;

    # return result with reversal reversed if needed.
    return $replace_right_to_left ? reverse $string : $string;

    }  # end sub replace_split_1()