The load_pha function can be called with just a filename and path argument, in which case the default id and use_errors equals false will be used. If header keywords for the associated background, ARF, or RMF are found. They will be read in as well. A PHA type II file will produce a individual data set for each spectrum. The generated identifiers for each spectrum's data set can be shown with 'list_data_ids'. Data set IDs can be integers or strings; in the latter case a string can denote useful information about the data (e.g., whether it is your source or background data set).