A study's named page patterns: sets of the report half's defaults
(report, page, header, footer, titles, footnotes, tokens) a report
chooses from. Standard is the blank rows; another pattern – the rows
whose output_id is @ and its name – says only what differs from
Standard. report_pattern() is a report's choice (NA: Standard),
set_report_pattern() sets it: the report's own rows stay over it.