docs: def _get_attribute_dimension(trait_name, mark_type=None):
      """Returns the dimension for the name of the trait for the specified mark.
  
      If `mark_type` is `None`, then the `trait_name` is returned
      as is.
      Returns `None` if the `trait_name` is not valid for `mark_type`.
      """
      if(mark_type is None):
          return trait_name
      scale_metadata = mark_type.class_traits()['scales_metadata']\
          .default_args[0]
      return scale_metadata.get(trait_name, {}).get('dimension', None)