Program:
    use XML::LibXSLT;
    my @result = XML::LibXSLT::xpath_to_string("title","Bob's Burgers");
    print $result[0]." is ".$result[1]."\n";

Output:
    title is concat('Bob', "'", 's Burgers', "'")

Correct Output:
    title is concat('Bob', "'", 's Burgers')

Commentary: This is caused because the fundamental parse operation is to append ' to chunks split by 
'.

My fix is:
        if ($value =~ /\'/) {
            $results[-1] = join('', 
                "concat(", 
                        join(', ', 
                                map { "'$_', \"'\"" }
                                split /\'/, $value), 
                                ")");
            # drop trailing ' if source string didn't have it
            if ($value !~ /'$/) {
              $results[-1] =~ s/, "\'"\)$/\)/;
            }
        }