def core_choice_fields(metadata_class):
fields = []<EOL>if metadata_class._meta.use_sites:<EOL><INDENT>fields.append('<STR_LIT>')<EOL><DEDENT>if metadata_class._meta.use_i18n:<EOL><INDENT>fields.append('<STR_LIT>')<EOL><DEDENT>return fields<EOL>
If the 'optional' core fields (_site and _language) are required, 
        list them here.