docs: def to_placeholder(self, name=None, db_type=None):
      """Returns a placeholder for the specified name, by applying the instance's format strings.
  
      :name: if None an unamed placeholder is returned, otherwise a named placeholder is returned.
      :db_type: if not None the placeholder is typecast.
      """
      if name is None:
        placeholder = self.unnamed_placeholder
      else:
        placeholder = self.named_placeholder.format(name)
  
      if db_type:
        return self.typecast(placeholder, db_type)
      else:
        return placeholder