code: def copy_out(source: Iterable[bytes], dest: io.BytesIO, use_placeholders: bool = False):
      
      for line in source:
          if use_placeholders:
              # True empty lines are assumed to be spurious as the placeholder
              # should be passed through
              if not line.strip():
                  continue
              if line.startswith(PLACEHOLDER):
                  line = b"\n"
          dest.write(line)
docs: Copy lines from source to destination.
  
      :param source: Source line iterable.
      :param dest: Destination open file.
      :param use_placeholders: When true, convert lines containing placeholders to
                               empty lines and drop true empty lines (assume to be
                               spuriously generated).