docs: def has_bom(self, filestream):
          """Check if has BOM."""
  
          content = filestream.read(4)
          if content == b'PK\x03\x04':
              # Zip file found.
              # Return `BINARY_ENCODE` as content is binary type,
              # but don't return None which means we don't know what we have.
              return filters.BINARY_ENCODE
          # We only handle zip files, so if we are checking this, we've already failed.
          return None