old_contents: """Iterables of DOT source code lines (including final newline)."""
  
  import typing
  
  from . import copying
  
  __all__ = ['Base']
  
  
  class LineIterable:
      """Iterable of DOT Source code lines
          (mimics ``file`` objects in text mode)."""
  
      def __iter__(self) -> typing.Iterator[str]:  # pragma: no cover
          r"""Yield the generated DOT source line by line.
  
          Yields: Line ending with a newline (``'\n'``).
          """
          raise NotImplementedError('to be implemented by concrete subclasses')
  
  
  # Common base interface for all exposed classes
  class Base(LineIterable, copying.Copy):
      """LineIterator with ``.source`` attribute, that it returns for ``str()``."""
  
      @property
      def source(self) -> str:  # pragma: no cover
          raise NotImplementedError('to be implemented by concrete subclasses')
  
      def __str__(self):
          """The DOT source code as string."""
          return self.source
  
new_contents: """Iterables of DOT source code lines (including final newline)."""
  
  import typing
  
  from . import copying
  
  __all__ = ['Base']
  
  
  class LineIterable:
      """Iterable of DOT Source code lines
          (mimics ``file`` objects in text mode)."""
  
      def __iter__(self) -> typing.Iterator[str]:  # pragma: no cover
          r"""Yield the generated DOT source line by line.
  
          Yields: Line ending with a newline (``'\n'``).
          """
          raise NotImplementedError('to be implemented by concrete subclasses')
  
  
  # Common base interface for all exposed classes
  class Base(LineIterable, copying.Copy):
      """LineIterator with ``.source`` attribute, that it returns for ``str()``."""
  
      @property
      def source(self) -> str:  # pragma: no cover
          raise NotImplementedError('to be implemented by concrete subclasses')
  
      def __str__(self) -> str:
          """The DOT source code as string."""
          return self.source
  
subject: add type annotation