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