docs: def _create_selector(int_type, func, trait, **kwargs):
      """Create a selector of the specified type.
  
      Also attaches the function `func` as an `on_trait_change` listener
      for the trait `trait` of the selector.
  
      This is an internal function which should not be called by the user.
  
      Parameters
      ----------
  
      int_type: type
          The type of selector to be added.
      func: function
          The call back function. It should take atleast two arguments. The name
          of the trait and the value of the trait are passed as arguments.
      trait: string
          The name of the Selector trait whose change triggers the
          call back function `func`.
      """
      interaction = _add_interaction(int_type, **kwargs)
      if func is not None:
          interaction.on_trait_change(func, trait)
      return interaction