A) sub default_handler {
          |
       B) |___| $rc = $self->convert_script_to_compiled_handler;
              |       |
              |       |___|  ....
       C)     |           | my $line = $self->get_mark_line;
       D)     |           | my $eval = join '' .....   <------ the join shown in my opening question above
       E)     |           | $rc = $self->compile(\$eval);
              |           |              |__
              |           |                 | ....
       F)     |           |                 |  eval $$eval;  <----- translated in   return $self->error_check;
              |           |                 |
              |           |
       G)     |           | $self->cache_it;
              |
       H)     | $rc = $self->run;
              |              | ....
       I)     |              | eval { $cv->($r, @_) };  ------->   JUMP INTO USER CODE  (here #line will not be understood)