old_contents: """Classes for class-based forward declaration."""
  
  
  class Forward(object):
      """Base class for autocomplete forward declaration."""
  
      def type(self):
          """Forward type. Should be implemented in subclasses."""
          raise NotImplementedError("Please use one of my subclasses")
  
      def to_dict(self):
          """Convert to dictionary which will be rendered as JSON."""
          return {
              "type": self.type
          }
  
  
  class Field(Forward):
      """Forward field value.
  
      .. py:attribute:: src
  
          The name of the form field whose value will be forwarded to a view.
  
      .. py:attribute:: dst
  
          The name of the key of the forwarded value from the src field in the
          forwarded dictionary. If this value is ``None``, then the key is
          ``src``.
      """
  
      type = "field"
  
      def __init__(self, src, dst=None):
          """Instantiate a forwarded field value."""
          self.src = src
          self.dst = dst
  
      def to_dict(self):
          """Convert to dictionary which will be rendered as JSON."""
          d = super(Field, self).to_dict()
  
          d.update(src=self.src)
          if self.dst is not None:
              d.update(dst=self.dst)
  
          return d
  
  
  class Const(Forward):
      """Forward arbitrary constant value.
  
      .. py:attribute:: val
  
          The value to forward. Must be JSON-serializable.
  
      .. py:attribute:: dst
  
          The name of the key of the forwarded value.
          ``src``.
      """
  
      type = "const"
  
      def __init__(self, val, dst):
          """Instantiate a forwarded constant value."""
          self.val = val
          self.dst = dst
  
      def to_dict(self):
          """Convert to dictionary which will be rendered as JSON."""
          d = super(Const, self).to_dict()
  
          d.update(val=self.val)
          d.update(dst=self.dst)
  
          return d
  
new_contents: """Classes for class-based forward declaration."""
  
  
  class Forward(object):
      """Base class for autocomplete forward declaration."""
  
      def type(self):
          """Forward type. Should be implemented in subclasses."""
          raise NotImplementedError("Please use one of my subclasses")
  
      def to_dict(self):
          """Convert to dictionary which will be rendered as JSON."""
          return {
              "type": self.type
          }
  
  
  class Field(Forward):
      """Forward field value.
  
      .. py:attribute:: src
  
          The name of the form field whose value will be forwarded to a view.
  
      .. py:attribute:: dst
  
          The name of the key of the forwarded value from the src field in the
          forwarded dictionary. If this value is ``None``, then the key is
          ``src``.
      """
  
      type = "field"
  
      def __init__(self, src, dst=None):
          """Instantiate a forwarded field value."""
          self.src = src
          self.dst = dst
  
      def to_dict(self):
          """Convert to dictionary which will be rendered as JSON."""
          d = super(Field, self).to_dict()
  
          d.update(src=self.src)
          if self.dst is not None:
              d.update(dst=self.dst)
  
          return d
  
  
  class Const(Forward):
      """Forward arbitrary constant value.
  
      .. py:attribute:: val
  
          The value to forward. Must be JSON-serializable.
  
      .. py:attribute:: dst
  
          The name of the key of the forwarded value.
      """
  
      type = "const"
  
      def __init__(self, val, dst):
          """Instantiate a forwarded constant value."""
          self.val = val
          self.dst = dst
  
      def to_dict(self):
          """Convert to dictionary which will be rendered as JSON."""
          d = super(Const, self).to_dict()
  
          d.update(val=self.val)
          d.update(dst=self.dst)
  
          return d
  
subject: Fix docstring typo