backward_async
Description:
[ Version ( since = "3.10" ) ]
public async bool backward_async (TextIter iter, Cancellable? cancellable, out TextIter match_start, out TextIter match_end, out bool has_wrapped_around) throws Error
  public async bool backward_async (TextIter iter, Cancellable? cancellable, out TextIter match_start, out TextIter match_end, out bool has_wrapped_around) throws Error
The asynchronous version of backward.
See the documentation of backward for more details.
See the AsyncResult documentation to know how to use this function.
If the operation is cancelled, the callback will only be called if cancellable was not 
        null. backward_async takes ownership of cancellable, so you can unref it after calling this 
      function.
Parameters:
| this | |
| iter | 
           start of search.  | 
      
| cancellable | 
           a Cancellable, or null.  | 
      
| callback | 
           a TaskReadyCallback to call when the operation is finished.  | 
      
| user_data | 
           the data to pass to the   |