This is the S3 generic method.
pk_add(pkproto_obj, pk_obj, objectname)
The `pk` object modified by the addition.
The `pkproto` object to be added
The `pk` object to which the `pkproto` object is to be added
The object name
[pk_add.pk_scales()] for the method for adding `pk_scales` objects (from [scale_conc()] and [scale_time()]); [pk_add.pk_settings_preprocess()] for the method for adding `pk_settings_preprocess` objects (from [settings_preprocess()]); [pk_add.pk_settings_data_info()] for the method for adding `pk_settings_data_info` objects (from [settings_data_info()]); [pk_add.pk_settings_optimx()] for the method for adding `pk_settings_optimx` objects (from [settings_optimx()]); [pk_add.pk_stat_model()] for the method for adding `pk_stat_model` objects (from `stat_model()`)