mask

Title   : mask
Usage   : $obj->mask(10,40,'Z');
          $obj->mask(10,40);
          $obj->mask($bio_location_obj, 'Z');
          $obj->mask($bio_location_obj);
Function: masks a sequence region by replacing the respective part with a
          custom character. If the character is omitted, 'X' in case of
          protein and 'N' in case of DNA/RNA alphabet is used to mask the
          sequence region.
Returns : the object it was invoked on
Args    : integer for start position
          integer for end position
          custom character to use for masking
                OR
          Bio::LocationI location for sequence region (strand NOT honored)
          custom character to use for masking