Method call walk-through
 
 
- Consider a simple prepare call:     $dbh->prepare(…)
- $dbh is reference to an object in the DBI::db class (regardless of driver)
- The DBI::db::prepare method is an alias for the DBI dispatch method
- DBI dispatch calls the driver’s own prepare method something like this:
- 
   my $inner_hash_ref = …     # from tie magic
 
 my $implementor_class = …  # from DBI magic data
 $inner_hash_ref->$implementor_class::prepare(...)
 
- Driver code gets the inner hash so it has fast access to the hash contents