Module:Citation/CS1/Date validation
--[[--------------------------&lt; F O R W A R D   D E C L A R A T I O N S &gt;--------------------------------------
 ]]
 
 local add_prop_cat, is_set, in_array, set_message, substitute, wrap_style;		-- imported functions from selected Module:Citation/CS1/Utilities
 local cfg;																		-- table of tables imported from selected Module:Citation/CS1/Configuration
 
 
 --[[--------------------------&lt; F I L E - S C O P E   D E C L A R A T I O N S &gt;--------------------------------
 
 File-scope variables are declared here
 
 ]]
 
 local lang_object = mw.getContentLanguage();									-- used by is_valid_accessdate(), is_valid_year(), date_name_xlate(); TODO: move to ~/Configuration?
 local year_limit;																-- used by is_valid_year()
 
 
 --[=[-------------------------&lt; I S _ V A L I D _ A C C E S S D A T E &gt;----------------------------------------
 
 returns true if:
 	Wikipedia start date &lt;= accessdate &lt; today + 2 days
 
 Wikipedia start date is 2001-01-15T00:00:00 UTC which is 979516800 seconds after 1970-01-01T00:00:00 UTC (the start of Unix time)
 accessdate is the date provided in |access-date= at time 00:00:00 UTC
 today is the current date at time 00:00:00 UTC plus 48 hours
 	if today is 2015-01-01T00:00:00 then
 		adding 24 hours gives 2015-01-02T00:00:00 – one second more than today
 		adding 24 hours gives 2015-01-03T00:00:00 – one second more than tomorrow
 
 This function does not work if it is fed month names for languages other than English.  Wikimedia #time: parser
 apparently doesn't understand non-English date month names. This function will always return false when the date
 contains a non-English month name because good1 is false after the call to lang.formatDate().  To get around that
 call this function with YYYY-MM-DD format dates.
 
 ]=]
 
 local function is_valid_accessdate (accessdate)
 	local good1, good2;
 	local access_ts, tomorrow_ts;												-- to hold Unix time stamps representing the dates
 
 	good1, access_ts = pcall (lang_object.formatDate, lang_object, 'U', accessdate );			-- convert accessdate value to Unix timestamp 
 	good2, tomorrow_ts = pcall (lang_object.formatDate, lang_object, 'U', 'today + 2 days' );	-- today midnight + 2 days is one second more than all day tomorrow
 	
 	if good1 and good2 then														-- lang.formatDate() returns a timestamp in the local script which which tonumber() may not understand
 		access_ts = tonumber (access_ts) or lang_object:parseFormattedNumber (access_ts);		-- convert to numbers for the comparison;
 		tomorrow_ts = tonumber (tomorrow_ts) or lang_object:parseFormattedNumber (tomorrow_ts);
 	else
 		return false;															-- one or both failed to convert to Unix time stamp
 	end
 
 	if 979516800 &lt;= access_ts and access_ts &lt; tomorrow_ts then					-- Wikipedia start date &lt;= accessdate &lt; tomorrow's date
 		return true;
 	else
 		return false;															-- accessdate out of range
 	end
 end
 
 
 --[[--------------------------&lt; G E T _ M O N T H _ N U M B E R &gt;----------------------------------------------
 
 returns a number according to the month in a date: 1 for January, etc.  Capitalization and spelling must be correct.
 If not a valid month, returns 0
 
 ]]
 
 local function get_month_number (month)
 	return cfg.date_names['local'].long[month] or cfg.date_names['local'].short[month] or	-- look for local names first
 			cfg.date_names['en'].long[month] or	cfg.date_names['en'].short[month] or		-- failing that, look for English names
 			0;																				-- not a recognized month name
 end
 
 
 --[[--------------------------&lt; G E T _ S E A S O N _ N U M B E R &gt;--------------------------------------------
 
 returns a number according to the sequence of seasons in a year: 21 for Spring, etc.  Capitalization and spelling
 must be correct. If not a valid season, returns 0.
 	21-24 = Spring, Summer, Autumn, Winter, independent of “Hemisphere”
 
 returns 0 when &lt;param&gt; is not |date=
 
 Season numbering is defined by Extended Date/Time Format (EDTF) specification (https://www.loc.gov/standards/datetime/)
 which became part of ISO 8601 in 2019.  See '§Sub-year groupings'.  The standard defines various divisions using
 numbers 21-41.  cs1|2 only supports generic seasons.  EDTF does support the distinction between north and south
 hemisphere seasons but cs1|2 has no way to make that distinction.
 
 These additional divisions not currently supported:
 	25-28 = Spring - Northern Hemisphere, Summer- Northern Hemisphere, Autumn - Northern Hemisphere, Winter - Northern Hemisphere
 	29-32 = Spring – Southern Hemisphere, Summer– Southern Hemisphere, Autumn – Southern Hemisphere, Winter - Southern Hemisphere
 	33-36 = Quarter 1, Quarter 2, Quarter 3, Quarter 4 (3 months each)
 	37-39 = Quadrimester 1, Quadrimester 2, Quadrimester 3 (4 months each)
 	40-41 = Semestral 1, Semestral-2 (6 months each)
 
 ]]
 
 local function get_season_number (season, param)
 	if 'date' ~= param then
 		return 0;																-- season dates only supported by |date=
 	end
 	return cfg.date_names['local'].season[season] or							-- look for local names first
 			cfg.date_names['en'].season[season] or								-- failing that, look for English names
 			0;																	-- not a recognized season name
 end
 
 
 --[[--------------------------&lt; G E T _ Q U A R T E R _ N U M B E R &gt;------------------------------------------
 
 returns a number according to the sequence of quarters in a year: 33 for first quarter, etc.  Capitalization and spelling
 must be correct. If not a valid quarter, returns 0.
 	33-36 = Quarter 1, Quarter 2, Quarter 3, Quarter 4 (3 months each)
 
 returns 0 when &lt;param&gt; is not |date=
 
 Quarter numbering is defined by Extended Date/Time Format (EDTF) specification (https://www.loc.gov/standards/datetime/)
 which became part of ISO 8601 in 2019.  See '§Sub-year groupings'.  The standard defines various divisions using
 numbers 21-41.  cs1|2 only supports generic seasons and quarters.
 
 These additional divisions not currently supported:
 	37-39 = Quadrimester 1, Quadrimester 2, Quadrimester 3 (4 months each)
 	40-41 = Semestral 1, Semestral-2 (6 months each)
 
 ]]
 
 local function get_quarter_number (quarter, param)
 	if 'date' ~= param then
 		return 0;																-- quarter dates only supported by |date=
 	end
 	quarter = mw.ustring.gsub (quarter, ' +', ' ');								-- special case replace multiple space chars with a single space char
 	return cfg.date_names['local'].quarter[quarter] or							-- look for local names first
 			cfg.date_names['en'].quarter[quarter] or							-- failing that, look for English names
 			0;																	-- not a recognized quarter name
 end
 
 
 --[[--------------------------&lt; G E T _ P R O P E R _ N A M E _ N U M B E R &gt;----------------------------------
 
 returns a non-zero number if date contains a recognized proper-name.  Capitalization and spelling must be correct.
 
 returns 0 when &lt;param&gt; is not |date=
 
 ]]
 
 local function get_proper_name_number (name, param)
 	if 'date' ~= param then
 		return 0;																-- proper-name dates only supported by |date=
 	end
 	return cfg.date_names['local'].named[name] or								-- look for local names dates first
 			cfg.date_names['en'].named[name] or									-- failing that, look for English names
 			0;																	-- not a recognized named date
 end
 
 
 --[[--------------------------&lt; G E T _ E L E M E N T _ N U M B E R &lt;------------------------------------------
 
 returns true if month or season or quarter or proper name is valid (properly spelled, capitalized, abbreviated)
 
 ]]
 
 local function get_element_number (element, param)
 	local num;
 	
 	local funcs = {get_month_number, get_season_number, get_quarter_number, get_proper_name_number};	-- list of functions to execute in order
 	
 	for _, func in ipairs (funcs) do											-- spin through the function list
 		num = func (element, param);											-- call the function and get the returned number
 		if 0 ~= num then														-- non-zero when valid month season quarter 
 			return num;															-- return that number
 		end
 	end
 	return nil;																	-- not valid
 end
 
 
 --[[--------------------------&lt; I S _ V A L I D _ Y E A R &gt;----------------------------------------------------
 
 Function gets current year from the server and compares it to year from a citation parameter.  Years more than one
 year in the future are not acceptable.
 
 Special case for |pmc-embargo-date=: years more than two years in the future are not acceptable
 
 ]]
 
 local function is_valid_year (year, param)
 	if not is_set (year_limit) then
 		year_limit = tonumber(os.date(&quot;%Y&quot;))+1;									-- global variable so we only have to fetch it once
 	end
 
 	year = tonumber (year) or lang_object:parseFormattedNumber (year);			-- convert to number for the comparison
 	if year and (100 &gt; year) then												-- years less than 100 not supported
 		return false;
 	end
 	
 	if 'pmc-embargo-date' == param then											-- special case for |pmc-embargo-date=
 		return year and (year &lt;= tonumber(os.date(&quot;%Y&quot;))+2) or false;			-- years more than two years in the future are not accepted
 	end	
 	return year and (year &lt;= year_limit) or false;
 end
 
 
 --[[--------------------------&lt; I S _ V A L I D _ D A T E &gt;----------------------------------------------------
 
 Returns true if day is less than or equal to the number of days in month and year is no farther into the future
 than next year; else returns false.
 
 Assumes Julian calendar prior to year 1582 and Gregorian calendar thereafter. Accounts for Julian calendar leap
 years before 1582 and Gregorian leap years after 1582. Where the two calendars overlap (1582 to approximately
 1923) dates are assumed to be Gregorian.
 
 ]]
 
 local function is_valid_date (year, month, day, param)
 local days_in_month = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 local month_length;
 	if not is_valid_year (year, param) then										-- no farther into the future than next year except |pmc-embargo-date= no more than two years in the future
 		return false;
 	end
 	
 	month = tonumber (month);													-- required for YYYY-MM-DD dates
 	
 	if (2 == month) then														-- if February
 		month_length = 28;														-- then 28 days unless
 		if 1582 &gt; tonumber(year) then											-- Julian calendar
 			if 0 == (year%4) then												-- is a leap year?
 				month_length = 29;												-- if leap year then 29 days in February
 			end
 		else																	-- Gregorian calendar
 			if (0 == (year%4) and (0 ~= (year%100) or 0 == (year%400))) then	-- is a leap year?
 				month_length = 29;												-- if leap year then 29 days in February
 			end
 		end
 	else
 		month_length = days_in_month[month];
 	end
 
 	if tonumber (day) &gt; month_length then
 		return false;
 	end
 	return true;
 end
 
 
 --[[--------------------------&lt; I S _ V A L I D _ M O N T H _ R A N G E _ S T Y L E &gt;--------------------------
 
 Months in a range are expected to have the same style: Jan–Mar or October–December but not February–Mar or Jul–August. 
 This function looks in cfg.date_names{} to see if both month names are listed in the long subtable or both are
 listed in the short subtable.  When both have the same style (both are listed in the same table), returns true; false else
 
 ]]
 
 local function is_valid_month_range_style (month1, month2)
 	if (cfg.date_names.en.long[month1] and cfg.date_names.en.long[month2]) or					-- are both English names listed in the long subtable?
 		(cfg.date_names.en.short[month1] and cfg.date_names.en.short[month2]) or				-- are both English names listed in the short subtable?
 		(cfg.date_names['local'].long[month1] and cfg.date_names['local'].long[month2]) or		-- are both local names listed in the long subtable?
 		(cfg.date_names['local'].short[month1] and cfg.date_names['local'].short[month2]) then	-- are both local names listed in the short subtable?
 			return true;
 	end
 	return false;																-- names are mixed
 end
 
 
 --[[--------------------------&lt; I S _ V A L I D _ M O N T H _ S E A S O N _ R A N G E &gt;------------------------
 
 Check a pair of months or seasons to see if both are valid members of a month or season pair.
 
 Month pairs are expected to be left to right, earliest to latest in time.
 
 All season ranges are accepted as valid because there are publishers out there who have published a Summer–Spring YYYY issue, hence treat as ok
 
 ]]
 
 local function is_valid_month_season_range(range_start, range_end, param)
 	local range_start_number = get_month_number (range_start);
 	local range_end_number;
 
 	if 0 == range_start_number then												-- is this a month range?
 		range_start_number = get_season_number (range_start, param);			-- not a month; is it a season? get start season number
 		range_end_number = get_season_number (range_end, param);				-- get end season number
 
 		if (0 ~= range_start_number) and (0 ~= range_end_number) and (range_start_number ~= range_end_number) then
 			return true;														-- any season pairing is accepted except when both are the same
 		end
 		return false;															-- range_start and/or range_end is not a season
 	end
 																				-- here when range_start is a month
 	range_end_number = get_month_number (range_end);							-- get end month number
 	if range_start_number &lt; range_end_number and								-- range_start is a month; does range_start precede range_end?
 		is_valid_month_range_style (range_start, range_end) then				-- do months have the same style?
 			return true;														-- proper order and same style
 	end
 	return false;																-- range_start month number is greater than or equal to range end number; or range end isn't a month
 end
 
 
 --[[--------------------------&lt; M A K E _ C O I N S _ D A T E &gt;------------------------------------------------
 
 This function receives a table of date parts for one or two dates and an empty table reference declared in
 Module:Citation/CS1.  The function is called only for |date= parameters and only if the |date=&lt;value&gt; is 
 determined to be a valid date format.  The question of what to do with invalid date formats is not answered here.
 
 The date parts in the input table are converted to an ISO 8601 conforming date string:
 	single whole dates:		yyyy-mm-dd
 	month and year dates:	yyyy-mm
 	year dates:				yyyy
 	ranges:					yyyy-mm-dd/yyyy-mm-dd
 							yyyy-mm/yyyy-mm
 							yyyy/yyyy
 
 Dates in the Julian calendar are reduced to year or year/year so that we don't have to do calendar conversion from
 Julian to Proleptic Gregorian.
 
 The input table has:
 	year, year2 – always present; if before 1582, ignore months and days if present
 	month, month2 – 0 if not provided, 1-12 for months, 21-24 for seasons; 99 Christmas
 	day, day2 –  0 if not provided, 1-31 for days
 	
 the output table receives:
 	rftdate:	an ISO 8601 formatted date
 	rftchron:	a free-form version of the date, usually without year which is in rftdate (season ranges and proper-name dates)
 	rftssn:		one of four season keywords: winter, spring, summer, fall (lowercase)
 	rftquarter:	one of four values: 1, 2, 3, 4
 
 ]]
 
 local function make_COinS_date (input, tCOinS_date)
 	local date;																	-- one date or first date in a range
 	local date2 = '';															-- end of range date
 	input.year = tonumber (input.year) or lang_object:parseFormattedNumber (input.year);	-- language-aware tonumber()
 	input.year2 = tonumber (input.year2) or lang_object:parseFormattedNumber (input.year2);	-- COinS dates are pseudo-ISO 8601 so convert to Arabic numerals
 
 -- start temporary Julian / Gregorian calendar uncertainty detection
 	local year = input.year;													-- this temporary code to determine the extent of sources dated to the Julian/Gregorian
 	local month = tonumber(input.month);										-- interstice 1 October 1582 – 1 January 1926
 	local day = tonumber (input.day);
 	if (0 ~= day) and															-- day must have a value for this to be a whole date
 		(((1582 == year) and (10 &lt;= month) and (12 &gt;= month)) or				-- any whole 1582 date from 1 October to 31 December or
 			((1926 == year) and (1 == month) and (1 == input.day)) or			-- 1 January 1926 or
 				((1582 &lt; year) and (1925 &gt;= year))) then						-- any date 1 January 1583 – 31 December 1925
 					tCOinS_date.inter_cal_cat = true;							-- set category flag true
 	end
 -- end temporary Julian / Gregorian calendar uncertainty detection
 	if ((1582 == year) and (10 &gt; month)) or (1582 &gt; year) then					-- if a Julian calendar date
 		tCOinS_date.rftdate = tostring (input.year);							-- &amp;rft.date gets year only
 		return;																	-- done
 	end
 																				-- here for all forms of Gregorian dates
 	if 20 &lt; tonumber (input.month) then											-- if season, quarter, or proper-name date
 		date = input.year;														-- &amp;rft.date gets year only
 		if 0 ~= input.year2 and input.year ~= input.year2 then					-- if a range, only the second year portion when not the same as range start year
 			date = string.format ('%.4d/%.4d', input.year, input.year2)			-- assemble the date range
 		end
 
 		local season = {[24] = 'winter', [21] = 'spring', [22] = 'summer', [23] = 'fall', [33] = '1', [34] = '2', [35] = '3', [36] = '4', [98] = 'Easter', [99] = 'Christmas'};	-- seasons lowercase, no autumn; proper-names use title case
 		if 0 == input.month2 then												-- single season, quarter, or proper-name date
 			if 40 &lt; tonumber(input.month) then
 				tCOinS_date.rftchron = season[input.month];						-- proper-name date; used in journal metadata only
 			elseif 30 &lt; tonumber(input.month) then
 				tCOinS_date.rftquarter = season[input.month];					-- quarter date; used in journal metadata only
 			else
 				tCOinS_date.rftssn = season[input.month];						-- season date; used in journal metadata only
 			end
 		else																	-- season ranges are lumped into &amp;rft.chron; &amp;rft.ssn and &amp;rft.quarter are left blank
 			if input.year ~= input.year2 then									-- season year – season year range or season year–year
 				if 0 ~= input.month2 then
 					tCOinS_date.rftchron = string.format ('%s %s – %s %s', season[input.month], input.year, season[input.month2], input.year2);	-- used in journal metadata only
 				end
 			else																-- season–season year range
 				tCOinS_date.rftchron = season[input.month] .. '–' .. season[input.month2];	-- season–season year range; used in journal metadata only
 			end
 		end
 
 		tCOinS_date.rftdate = tostring (date);
 		return;																	-- done
 	end
 																				-- here for gregorian calendar dates
 	if 0 ~= input.day then
 		date = string.format ('%s-%.2d-%.2d', input.year, tonumber(input.month), tonumber(input.day));	-- whole date
 	elseif 0 ~= input.month then
 		date = string.format ('%s-%.2d', input.year, tonumber(input.month));	-- year and month
 	else
 		date = string.format ('%s', input.year);								-- just year
 	end
 
 	if 0 ~= input.year2 then
 		if 0 ~= input.day2 then
 			date2 = string.format ('/%s-%.2d-%.2d', input.year2, tonumber(input.month2), tonumber(input.day2));		-- whole date
 		elseif 0 ~= input.month2 then
 			date2 = string.format ('/%s-%.2d', input.year2, tonumber(input.month2));	-- year and month
 		else
 			date2 = string.format ('/%s', input.year2);							-- just year
 		end
 	end
 	
 	tCOinS_date.rftdate = date .. date2;										-- date2 has the '/' separator
 	return;
 end
 
 
 --[[--------------------------&lt; P A T T E R N S &gt;--------------------------------------------------------------
 
 this is the list of patterns for date formats that this module recognizes.  Approximately the first half of these
 patterns represent formats that might be reformatted into another format.  Those that might be reformatted have
 'indicator' letters that identify the content of the matching capture: 'd' (day), 'm' (month), 'a' (anchor year),
 'y' (year); second day, month, year have a '2' suffix.
 
 These patterns are used for both date validation and for reformatting.  This table should not be moved to ~/Configuration
 because changes to this table require changes to check_date() and to reformatter() and reformat_date()
 
 ]]
 
 local patterns = {
 	 																			-- year-initial numerical year-month-day
 	['ymd'] = {'^(%d%d%d%d)%-(%d%d)%-(%d%d)$', 'y', 'm', 'd'},					
 																				-- month-initial: month day, year
 	['Mdy'] = {'^(%D-) +([1-9]%d?), +((%d%d%d%d?)%a?)$', 'm', 'd', 'a', 'y'},
 																				-- month-initial day range: month day–day, year; days are separated by endash
 	['Md-dy'] = {'^(%D-) +([1-9]%d?)[%-–]([1-9]%d?), +((%d%d%d%d)%a?)$', 'm', 'd', 'd2', 'a', 'y'},
 																				-- day-initial: day month year
 	['dMy'] = {'^([1-9]%d?) +(%D-) +((%d%d%d%d?)%a?)$', 'd', 'm', 'a', 'y'},
 																				-- year-initial: year month day; day: 1 or 2 two digits, leading zero allowed; not supported at en.wiki
 	--	['yMd'] = {'^((%d%d%d%d?)%a?) +(%D-) +(%d%d?)$', 'a', 'y', 'm', 'd'},
 																				-- day-range-initial: day–day month year; days are separated by endash
 	['d-dMy'] = {'^([1-9]%d?)[%-–]([1-9]%d?) +(%D-) +((%d%d%d%d)%a?)$', 'd', 'd2', 'm', 'a', 'y'},
 																				-- day initial month-day-range: day month - day month year; uses spaced endash
 	['dM-dMy'] = {'^([1-9]%d?) +(%D-) +[%-–] +([1-9]%d?) +(%D-) +((%d%d%d%d)%a?)$', 'd', 'm', 'd2', 'm2', 'a', 'y'},
 																				-- month initial month-day-range: month day – month day, year;  uses spaced endash
 	['Md-Mdy'] = {'^(%D-) +([1-9]%d?) +[%-–] +(%D-) +([1-9]%d?), +((%d%d%d%d)%a?)$','m', 'd', 'm2', 'd2', 'a', 'y'},
 																				-- day initial month-day-year-range: day month year - day month year; uses spaced endash
 	['dMy-dMy'] = {'^([1-9]%d?) +(%D-) +(%d%d%d%d) +[%-–] +([1-9]%d?) +(%D-) +((%d%d%d%d)%a?)$', 'd', 'm', 'y', 'd2', 'm2', 'a', 'y2'},
 																				-- month initial month-day-year-range: month day, year – month day, year;  uses spaced endash
 	['Mdy-Mdy'] = {'^(%D-) +([1-9]%d?), +(%d%d%d%d) +[%-–] +(%D-) +([1-9]%d?), +((%d%d%d%d)%a?)$', 'm', 'd', 'y', 'm2', 'd2', 'a', 'y2'},
 
 																				-- these date formats cannot be converted, per se, but month name can be rendered short or long
 																				-- month/season year - month/season year; separated by spaced endash
 	['My-My'] = {'^(%D-) +(%d%d%d%d) +[%-–] +(%D-) +((%d%d%d%d)%a?)$', 'm', 'y', 'm2', 'a', 'y2'},
 																				-- month/season range year; months separated by endash
 	['M-My'] = {'^(%D-)[%-–](%D-) +((%d%d%d%d)%a?)$', 'm', 'm2', 'a', 'y'},
 																				-- month/season year or proper-name year; quarter year when First Quarter YYYY etc.
 	['My'] = {'^([^%d–]-) +((%d%d%d%d)%a?)$', 'm', 'a', 'y'},					-- this way because endash is a member of %D; %D- will match January–March 2019 when it shouldn't
 
 																				-- these date formats cannot be converted
 	['Sy4-y2'] = {'^(%D-) +((%d%d)%d%d)[%-–]((%d%d)%a?)$'},						-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
 	['Sy-y'] = {'^(%D-) +(%d%d%d%d)[%-–]((%d%d%d%d)%a?)$'},						-- special case Winter/Summer year-year; year separated with unspaced endash
 	['y-y'] = {'^(%d%d%d%d?)[%-–]((%d%d%d%d?)%a?)$'},							-- year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
 	['y4-y2'] = {'^((%d%d)%d%d)[%-–]((%d%d)%a?)$'},								-- year range: YYYY–YY; separated by unspaced endash
 	['y'] = {'^((%d%d%d%d?)%a?)$'},												-- year; here accept either YYY or YYYY
 	}
 
 
 --[[--------------------------&lt; I S _ V A L I D _ E M B A R G O _ D A T E &gt;------------------------------------
 
 returns true and date value if that value has proper dmy, mdy, ymd format.
 
 returns false and 9999 (embargoed forever) when date value is not proper format; assumes that when |pmc-embargo-date= is
 set, the editor intended to embargo a PMC but |pmc-embargo-date= does not hold a single date.
 
 ]]
 
 local function is_valid_embargo_date (v)
 	if v:match (patterns['ymd'][1]) or											-- ymd
 		v:match (patterns['Mdy'][1]) or											-- dmy
 		v:match (patterns['dMy'][1]) then										-- mdy
 			return true, v;
 	end
 	return false, '9999';														-- if here not good date so return false and set embargo date to long time in future
 end
 
 
 --[[--------------------------&lt; C H E C K _ D A T E &gt;----------------------------------------------------------
 
 Check date format to see that it is one of the formats approved by WP:DATESNO or WP:DATERANGE. Exception: only
 allowed range separator is endash.  Additionally, check the date to see that it is a real date: no 31 in 30-day
 months; no 29 February when not a leap year.  Months, both long-form and three character abbreviations, and seasons
 must be spelled correctly.  Future years beyond next year are not allowed.
 
 If the date fails the format tests, this function returns false and does not return values for anchor_year and
 COinS_date.  When this happens, the date parameter is (DEBUG: not?) used in the COinS metadata and the CITEREF identifier gets
 its year from the year parameter if present otherwise CITEREF does not get a date value.
 
 Inputs:
 	date_string - date string from date-holding parameters (date, year, publication-date, access-date, pmc-embargo-date, archive-date, lay-date)
 
 Returns:
 	false if date string is not a real date; else
 	true, anchor_year, COinS_date
 		anchor_year can be used in CITEREF anchors
 		COinS_date is ISO 8601 format date; see make_COInS_date()
 
 ]]
 
 local function check_date (date_string, param, tCOinS_date)
 	local year;																	-- assume that year2, months, and days are not used;
 	local year2 = 0;															-- second year in a year range
 	local month = 0;
 	local month2 = 0;															-- second month in a month range
 	local day = 0;
 	local day2 = 0;																-- second day in a day range
 	local anchor_year;
 	local coins_date;
 
 	if date_string:match (patterns['ymd'][1]) then								-- year-initial numerical year month day format
 		year, month, day = date_string:match (patterns['ymd'][1]);
 		if 12 &lt; tonumber(month) or 1 &gt; tonumber(month) or 1582 &gt; tonumber(year) or 0 == tonumber(day) then return false; end	-- month or day number not valid or not Gregorian calendar
 		anchor_year = year;
 	
 	elseif mw.ustring.match(date_string, patterns['Mdy'][1]) then				-- month-initial: month day, year
 		month, day, anchor_year, year = mw.ustring.match(date_string, patterns['Mdy'][1]);
 		month = get_month_number (month);
 		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
 				
 	elseif mw.ustring.match(date_string, patterns['Md-dy'][1]) then				-- month-initial day range: month day–day, year; days are separated by endash
 		month, day, day2, anchor_year, year = mw.ustring.match(date_string, patterns['Md-dy'][1]);
 		if tonumber(day) &gt;= tonumber(day2) then return false; end				-- date range order is left to right: earlier to later; dates may not be the same;
 		month = get_month_number (month);
 		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
 		month2=month;															-- for metadata
 		year2 = year;
 
 	elseif mw.ustring.match(date_string, patterns['dMy'][1]) then				-- day-initial: day month year
 		day, month, anchor_year, year = mw.ustring.match(date_string, patterns['dMy'][1]);
 		month = get_month_number (month);
 		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
 
 --[[ NOT supported at en.wiki
 	elseif mw.ustring.match(date_string, patterns['yMd'][1]) then				-- year-initial: year month day; day: 1 or 2 two digits, leading zero allowed
 		anchor_year, year, month, day = mw.ustring.match(date_string, patterns['yMd'][1]);
 		month = get_month_number (month);
 		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
 -- end NOT supported at en.wiki ]]
 
 	elseif mw.ustring.match(date_string, patterns['d-dMy'][1]) then				-- day-range-initial: day–day month year; days are separated by endash
 		day, day2, month, anchor_year, year = mw.ustring.match(date_string, patterns['d-dMy'][1]);
 		if tonumber(day) &gt;= tonumber(day2) then return false; end				-- date range order is left to right: earlier to later; dates may not be the same;
 		month = get_month_number (month);
 		if 0 == month then return false; end									-- return false if month text isn't one of the twelve months
 		month2 = month;															-- for metadata
 		year2 = year;
 
 	elseif mw.ustring.match(date_string, patterns['dM-dMy'][1]) then			-- day initial month-day-range: day month - day month year; uses spaced endash
 		day, month, day2, month2, anchor_year, year = mw.ustring.match(date_string, patterns['dM-dMy'][1]);
 		if (not is_valid_month_season_range(month, month2)) or not is_valid_year(year) then return false; end	-- date range order is left to right: earlier to later;
 		month = get_month_number (month);										-- for metadata
 		month2 = get_month_number (month2);
 		year2 = year;
 
 	elseif mw.ustring.match(date_string, patterns['Md-Mdy'][1]) then			-- month initial month-day-range: month day – month day, year; uses spaced endash
 		month, day, month2, day2, anchor_year, year = mw.ustring.match(date_string, patterns['Md-Mdy'][1]);
 		if (not is_valid_month_season_range(month, month2, param)) or not is_valid_year(year) then return false; end
 		month = get_month_number (month);										-- for metadata
 		month2 = get_month_number (month2);
 		year2 = year;
 
 	elseif mw.ustring.match(date_string, patterns['dMy-dMy'][1]) then			-- day initial month-day-year-range: day month year - day month year; uses spaced endash
 		day, month, year, day2, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['dMy-dMy'][1]);
 		if tonumber(year2) &lt;= tonumber(year) then return false; end				-- must be sequential years, left to right, earlier to later
 		if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end		-- year2 no more than one year in the future; months same style
 		month = get_month_number (month);										-- for metadata
 		month2 = get_month_number (month2);
 		if 0 == month or 0 == month2 then return false; end						-- both must be valid
 
 	elseif mw.ustring.match(date_string, patterns['Mdy-Mdy'][1]) then			-- month initial month-day-year-range: month day, year – month day, year; uses spaced endash
 		month, day, year, month2, day2, anchor_year, year2 = mw.ustring.match(date_string, patterns['Mdy-Mdy'][1]);
 		if tonumber(year2) &lt;= tonumber(year) then return false; end				-- must be sequential years, left to right, earlier to later
 		if not is_valid_year(year2) or not is_valid_month_range_style(month, month2) then return false; end		-- year2 no more than one year in the future; months same style
 		month = get_month_number (month);										-- for metadata
 		month2 = get_month_number(month2);
 		if 0 == month or 0 == month2 then return false; end						-- both must be valid
 
 	elseif mw.ustring.match(date_string, patterns['Sy4-y2'][1]) then			-- special case Winter/Summer year-year (YYYY-YY); year separated with unspaced endash
 		local century;
 		month, year, century, anchor_year, year2 = mw.ustring.match(date_string, patterns['Sy4-y2'][1]);
 		if 'Winter' ~= month and 'Summer' ~= month then return false end;		-- 'month' can only be Winter or Summer
 		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor_year from both years
 		year2 = century..year2;													-- add the century to year2 for comparisons
 		if 1 ~= tonumber(year2) - tonumber(year) then return false; end			-- must be sequential years, left to right, earlier to later
 		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
 		month = get_season_number(month, param);
 
 	elseif mw.ustring.match(date_string, patterns['Sy-y'][1]) then				-- special case Winter/Summer year-year; year separated with unspaced endash
 		month, year, anchor_year, year2 = mw.ustring.match(date_string, patterns['Sy-y'][1]);
 		month = get_season_number (month, param);								-- &lt;month&gt; can only be winter or summer; also for metadata
 		if (month ~= cfg.date_names['en'].season['Winter']) and (month ~= cfg.date_names['en'].season['Summer']) then
 			return false;														-- not Summer or Winter; abandon
 		end
 		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor_year from both years
 		if 1 ~= tonumber(year2) - tonumber(year) then return false; end			-- must be sequential years, left to right, earlier to later
 		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
 
 	elseif mw.ustring.match(date_string, patterns['My-My'][1]) then				-- month/season year - month/season year; separated by spaced endash
 		month, year, month2, anchor_year, year2 = mw.ustring.match(date_string, patterns['My-My'][1]);
 		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor_year from both years
 		if tonumber(year) &gt;= tonumber(year2) then return false; end				-- left to right, earlier to later, not the same
 		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
 		if 0 ~= get_month_number(month) and 0 ~= get_month_number(month2) and is_valid_month_range_style(month, month2) then 	-- both must be month year, same month style
 			month = get_month_number(month);
 			month2 = get_month_number(month2);
 		elseif 0 ~= get_season_number(month, param) and 0 ~= get_season_number(month2, param) then	-- both must be season year, not mixed
 			month = get_season_number(month, param);
 			month2 = get_season_number(month2, param);
 		else
 			 return false;
 		end
 
 	elseif mw.ustring.match(date_string, patterns['M-My'][1]) then				-- month/season range year; months separated by endash 
 		month, month2, anchor_year, year = mw.ustring.match(date_string, patterns['M-My'][1]);
 		if (not is_valid_month_season_range(month, month2, param)) or (not is_valid_year(year)) then return false; end
 		if 0 ~= get_month_number(month) then									-- determined to be a valid range so just check this one to know if month or season
 			month = get_month_number(month);
 			month2 = get_month_number(month2);
 			if 0 == month or 0 == month2 then return false; end
 		else
 			month = get_season_number(month, param);
 			month2 = get_season_number(month2, param);
 		end
 		year2 = year;
 		
 	elseif mw.ustring.match(date_string, patterns['My'][1]) then				-- month/season/quarter/proper-name year
 		month, anchor_year, year = mw.ustring.match(date_string, patterns['My'][1]);
 		if not is_valid_year(year) then return false; end
 		month = get_element_number(month, param);								-- get month season quarter proper-name number or nil
 		if not month then return false; end										-- not valid whatever it is
 
 	elseif mw.ustring.match(date_string, patterns['y-y'][1]) then				-- Year range: YYY-YYY or YYY-YYYY or YYYY–YYYY; separated by unspaced endash; 100-9999
 		year, anchor_year, year2 = mw.ustring.match(date_string, patterns['y-y'][1]);
 		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor year from both years
 		if tonumber(year) &gt;= tonumber(year2) then return false; end				-- left to right, earlier to later, not the same
 		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
 
 	elseif mw.ustring.match(date_string, patterns['y4-y2'][1]) then				-- Year range: YYYY–YY; separated by unspaced endash
 		local century;
 		year, century, anchor_year, year2 = mw.ustring.match(date_string, patterns['y4-y2'][1]);
 		anchor_year = year .. '–' .. anchor_year;								-- assemble anchor year from both years
 
 		if 13 &gt; tonumber(year2) then return false; end							-- don't allow 2003-05 which might be May 2003
 		year2 = century .. year2;												-- add the century to year2 for comparisons
 		if tonumber(year) &gt;= tonumber(year2) then return false; end				-- left to right, earlier to later, not the same
 		if not is_valid_year(year2) then return false; end						-- no year farther in the future than next year
 
 		if in_array (param, {'date', 'publication-date', 'year'}) then			-- here when 'valid' abbreviated year range; if one of these parameters
 			add_prop_cat ('year-range-abbreviated');							-- add properties cat
 		end
 
 	elseif mw.ustring.match(date_string, patterns['y'][1]) then					-- year; here accept either YYY or YYYY
 		anchor_year, year = mw.ustring.match(date_string, patterns['y'][1]);
 		if false == is_valid_year(year) then
 			return false;
 		end
 
 	else
 		return false;															-- date format not one of the MOS:DATE approved formats
 	end
 
 	if param ~= 'date' then														-- CITEREF disambiguation only allowed in |date=; |year= &amp; |publication-date= promote to date
 		if anchor_year:match ('%l$') then
 			return false;
 		end
 	end
 
 	if 'access-date' == param then												-- test access-date here because we have numerical date parts
 		if 0 ~= year and 0 ~= month and 0 ~= day and 							-- all parts of a single date required
 			0 == year2 and 0 == month2 and 0 == day2 then						-- none of these; access-date must not be a range
 				if not is_valid_accessdate(year .. '-' .. month .. '-' .. day) then	
 					return false;												-- return false when access-date out of bounds
 				end
 		else
 			return false;														-- return false when access-date is a range of two dates
 		end
 	end
 
 	if 'archive-date' == param then												-- test archive-date here because we have numerical date parts
 		if not (0 ~= year and 0 ~= month and 0 ~= day and						-- all parts of a single date required
 			0 == year2 and 0 == month2 and 0 == day2) then						-- none of these; archive-date must not be a range
 				return false;													-- return false when archive-date is a range of two dates
 		end
 	end
 
 	local result=true;															-- check whole dates for validity; assume true because not all dates will go through this test
 	if 0 ~= year and 0 ~= month and 0 ~= day and 0 == year2 and 0 == month2 and 0 == day2 then		-- YMD (simple whole date)
 		result = is_valid_date (year, month, day, param);						-- &lt;param&gt; for |pmc-embargo-date=
 
 	elseif 0 ~= year and 0 ~= month and 0 ~= day and 0 == year2 and 0 == month2 and 0 ~= day2 then	-- YMD-d (day range)
 		result = is_valid_date (year, month, day);
 		result = result and is_valid_date (year, month, day2);
 
 	elseif 0 ~= year and 0 ~= month and 0 ~= day and 0 == year2 and 0 ~= month2 and 0 ~= day2 then	-- YMD-md (day month range)
 		result = is_valid_date (year, month, day);
 		result = result and is_valid_date (year, month2, day2);
 
 	elseif 0 ~= year and 0 ~= month and 0 ~= day and 0 ~= year2 and 0 ~= month2 and 0 ~= day2 then	-- YMD-ymd (day month year range)
 		result = is_valid_date(year, month, day);
 		result = result and is_valid_date(year2, month2, day2);
 	end
 	
 	if false == result then return false; end
 
 	if nil ~= tCOinS_date then													-- this table only passed into this function when testing |date= parameter values
 		make_COinS_date ({year = year, month = month, day = day, year2 = year2, month2 = month2, day2 = day2}, tCOinS_date);	-- make an ISO 8601 date string for COinS
 	end
 	
 	return true, anchor_year;													-- format is good and date string represents a real date
 end	
 
 
 --[[--------------------------&lt; D A T E S &gt;--------------------------------------------------------------------
 
 Cycle the date-holding parameters in passed table date_parameters_list through check_date() to check compliance with MOS:DATE. For all valid dates, check_date() returns
 true. The |date= parameter test is unique, it is the only date holding parameter from which values for anchor_year (used in CITEREF identifiers) and COinS_date (used in
 the COinS metadata) are derived.  The |date= parameter is the only date-holding parameter that is allowed to contain the no-date keywords &quot;n.d.&quot; or &quot;nd&quot; (without quotes).
 
 Unlike most error messages created in this module, only one error message is created by this function. Because all of the date holding parameters are processed serially,
 parameters with errors are added to the &lt;error_list&gt; sequence table as the dates are tested.
 
 ]]
 
 local function dates(date_parameters_list, tCOinS_date, error_list)
 	local anchor_year;															-- will return as nil if the date being tested is not |date=
 	local COinS_date;															-- will return as nil if the date being tested is not |date=
 	local embargo_date;															-- if embargo date is a good dmy, mdy, ymd date then holds original value else reset to 9999
 	local good_date = false;
 
 	for k, v in pairs(date_parameters_list) do									-- for each date-holding parameter in the list
 		if is_set(v.val) then													-- if the parameter has a value
 			v.val = mw.ustring.gsub(v.val, '%d', cfg.date_names.local_digits);	-- translate 'local' digits to Western 0-9
 			if v.val:match(&quot;^c%. [1-9]%d%d%d?%a?$&quot;) then						-- special case for c. year or with or without CITEREF disambiguator - only |date= and |year=
 				local year = v.val:match(&quot;c%. ([1-9]%d%d%d?)%a?&quot;);				-- get the year portion so it can be tested
 				if 'date' == k then
 					anchor_year, COinS_date = v.val:match(&quot;((c%. [1-9]%d%d%d?)%a?)&quot;);	-- anchor year and COinS_date only from |date= parameter
 					good_date = is_valid_year(year);
 				elseif 'year' == k then
 					good_date = is_valid_year(year);
 				end
 			elseif 'date' == k then												-- if the parameter is |date=
 				if v.val:match(&quot;^n%.d%.%a?$&quot;) then -- ToDo: I18N								-- if |date=n.d. with or without a CITEREF disambiguator
 					good_date, anchor_year, COinS_date = true, v.val:match(&quot;((n%.d%.)%a?)&quot;); -- ToDo: I18N	-- &quot;n.d.&quot;; no error when date parameter is set to no date
 				elseif v.val:match(&quot;^nd%a?$&quot;) then -- ToDo: I18N								-- if |date=nd with or without a CITEREF disambiguator
 					good_date, anchor_year, COinS_date = true, v.val:match(&quot;((nd)%a?)&quot;); -- ToDo: I18N	-- &quot;nd&quot;;	no error when date parameter is set to no date
 				else
 					good_date, anchor_year, COinS_date = check_date (v.val, k, tCOinS_date);	-- go test the date
 				end
 			elseif 'year' == k then												-- if the parameter is |year= it should hold only a year value
 				if v.val:match(&quot;^[1-9]%d%d%d?%a?$&quot;) then						-- if |year = 3 or 4 digits only with or without a CITEREF disambiguator
 					good_date, anchor_year, COinS_date = true, v.val:match(&quot;((%d+)%a?)&quot;);
 				end
 			elseif 'pmc-embargo-date' == k then									-- if the parameter is |pmc-embargo-date=
 				good_date = check_date (v.val, k);								-- go test the date
 				if true == good_date then										-- if the date is a valid date
 					good_date, embargo_date = is_valid_embargo_date (v.val);	-- is |pmc-embargo-date= date a single dmy, mdy, or ymd formatted date? yes: returns embargo date; no: returns 9999
 				end
 			else																-- any other date-holding parameter
 				good_date = check_date (v.val, k);								-- go test the date
 			end
 			if false == good_date then											-- assemble one error message so we don't add the tracking category multiple times
 				table.insert (error_list, wrap_style ('parameter', v.name));	-- make parameter name suitable for error message list
 			end
 		end
 	end
 	return anchor_year, embargo_date;											-- and done
 end
 
 
 --[[--------------------------&lt; Y E A R _ D A T E _ C H E C K &gt;------------------------------------------------
 
 Compare the value provided in |year= with the year value(s) provided in |date=.  This function sets a local numeric value:
 	0 - year value does not match the year value in date
 	1 - (default) year value matches the year value in date or one of the year values when date contains two years
 	2 - year value matches the year value in date when date is in the form YYYY-MM-DD and year is disambiguated (|year=YYYYx)
 
 the numeric value in &lt;result&gt; determines the 'output' if any from this function:
 	0 – adds error message to error_list sequence table
 	1 – adds maint cat
 	2 – does nothing
 
 ]]
 
 local function year_date_check (year_string, year_origin, date_string, date_origin, error_list)
 	local year;
 	local date1;
 	local date2;
 	local result = 1;															-- result of the test; assume that the test passes
 
 	year = year_string:match ('(%d%d%d%d?)');
 
 	if date_string:match ('%d%d%d%d%-%d%d%-%d%d') and year_string:match ('%d%d%d%d%a') then	--special case where both date and year are required YYYY-MM-DD and YYYYx
 		date1 = date_string:match ('(%d%d%d%d)');
 		year = year_string:match ('(%d%d%d%d)');
 		if year ~= date1 then
 			result = 0;															-- years don't match
 		else
 			result = 2;															-- years match; but because disambiguated, don't add to maint cat
 		end
 		
 	elseif date_string:match (&quot;%d%d%d%d?.-%d%d%d%d?&quot;) then						-- any of the standard range formats of date with two three- or four-digit years
 		date1, date2 = date_string:match (&quot;(%d%d%d%d?).-(%d%d%d%d?)&quot;);
 		if year ~= date1 and year ~= date2 then
 			result = 0;
 		end
 
 	elseif mw.ustring.match(date_string, &quot;%d%d%d%d[%-–]%d%d&quot;) then				-- YYYY-YY date ranges
 		local century;
 		date1, century, date2 = mw.ustring.match(date_string, &quot;((%d%d)%d%d)[%-–]+(%d%d)&quot;);
 		date2 = century..date2;													-- convert YY to YYYY
 		if year ~= date1 and year ~= date2 then
 			result = 0;
 		end
 
 	elseif date_string:match (&quot;%d%d%d%d?&quot;) then									-- any of the standard formats of date with one year
 		date1 = date_string:match (&quot;(%d%d%d%d?)&quot;);
 		if year ~= date1 then
 			result = 0;
 		end
 	else																		-- should never get here; this function called only when no other date errors
 		result = 0;																-- no recognizable year in date
 	end
 
 	if 0 == result then															-- year / date mismatch
 		table.insert (error_list, substitute (cfg.messages['mismatch'], {year_origin, date_origin}));	-- add error message to error_list sequence table
 	elseif 1 == result then														-- redundant year / date
 		set_message ('maint_date_year');										-- add a maint cat
 	end
 end
 
 
 --[[--------------------------&lt; R E F O R M A T T E R &gt;--------------------------------------------------------
 
 reformat 'date' into new format specified by format_param if pattern_idx (the current format of 'date') can be
 reformatted.  Does the grunt work for reformat_dates().
 
 The table re_formats maps pattern_idx (current format) and format_param (desired format) to a table that holds:
 	format string used by string.format()
 	identifier letters ('d', 'm', 'y', 'd2', 'm2', 'y2') that serve as indexes into a table t{} that holds captures
 		from mw.ustring.match() for the various date parts specified by  patterns[pattern_idx][1]
 
 Items in patterns{} have the general form:
 	['ymd'] = {'^(%d%d%d%d)%-(%d%d)%-(%d%d)$', 'y', 'm', 'd'}, where:
 		['ymd'] is pattern_idx
 		patterns['ymd'][1] is the match pattern with captures for mw.ustring.match()
 		patterns['ymd'][2] is an indicator letter identifying the content of the first capture
 		patterns['ymd'][3] ... the second capture etc.
 
 when a pattern matches a date, the captures are loaded into table t{} in capture order using the idemtifier
 characters as indexes into t{}  For the above, a ymd date is in t{} as:
 	t.y = first capture (year), t.m = second capture (month), t.d = third capture (day)
 
 To reformat, this function is called with the pattern_idx that matches the current format of the date and with
 format_param set to the desired format.  This function loads table t{} as described and then calls string.format()
 with the format string specified by re_format[pattern_idx][format_param][1] using values taken from t{} according
 to the capture identifier letters specified by patterns[pattern_idx][format_param][n] where n is 2..
 
 ]]
 
 local re_formats = {
 	['ymd'] = {																	-- date format is ymd; reformat to:
 		['mdy'] = {'%s %s, %s', 'm', 'd', 'y'},									-- |df=mdy
 		['dmy'] = {'%s %s %s', 'd', 'm', 'y'},									-- |df=dmy
 	--		['yMd'] = {'%s %s %s', 'y', 'm', 'd'},								-- |df=yMd; not supported at en.wiki
 		},
 	['Mdy'] = {																	-- date format is Mdy; reformat to:
 		['mdy'] = {'%s %s, %s', 'm', 'd', 'y'},									-- for long/short reformatting
 		['dmy'] = {'%s %s %s', 'd', 'm', 'y'},									-- |df=dmy
 		['ymd'] = {'%s-%s-%s', 'y', 'm', 'd'},									-- |df=ymd
 	--		['yMd'] = {'%s %s %s', 'y', 'm', 'd'},								-- |df=yMd; not supported at en.wiki
 		},
 	['dMy'] = {																	-- date format is dMy; reformat to:
 		['dmy'] = {'%s %s %s', 'd', 'm', 'y'},									-- for long/short reformatting
 		['mdy'] = {'%s %s, %s', 'm', 'd', 'y'},									-- |df=mdy
 		['ymd'] = {'%s-%s-%s', 'y', 'm', 'd'},									-- |df=ymd
 	--		['yMd'] = {'%s %s %s', 'y', 'm', 'd'},								-- |df=yMd; not supported at en.wiki
 		},
 	['Md-dy'] = {																-- date format is Md-dy; reformat to:
 		['mdy'] = {'%s %s–%s, %s', 'm', 'd', 'd2', 'y'},						-- for long/short reformatting
 		['dmy'] = {'%s–%s %s %s', 'd', 'd2', 'm', 'y'},							-- |df=dmy -&gt; d-dMy 
 		},
 	['d-dMy'] = {																-- date format is d-d&gt;y; reformat to:
 		['dmy'] = {'%s–%s %s %s', 'd', 'd2', 'm', 'y'},							-- for long/short reformatting
 		['mdy'] = {'%s %s–%s, %s', 'm', 'd', 'd2', 'y'},						-- |df=mdy -&gt; Md-dy 
 		},
 	['dM-dMy'] = {																-- date format is dM-dMy; reformat to:
 		['dmy'] = {'%s %s – %s %s %s', 'd', 'm', 'd2', 'm2', 'y'},				-- for long/short reformatting
 		['mdy'] = {'%s %s – %s %s, %s', 'm', 'd', 'm2', 'd2', 'y'},				-- |df=mdy -&gt; Md-Mdy 
 		},
 	['Md-Mdy'] = {																-- date format is Md-Mdy; reformat to:
 		['mdy'] = {'%s %s – %s %s, %s', 'm', 'd',  'm2', 'd2', 'y'},			-- for long/short reformatting
 		['dmy'] = {'%s %s – %s %s %s', 'd', 'm', 'd2', 'm2', 'y'},				-- |df=dmy -&gt; dM-dMy 
 		},
 	['dMy-dMy'] = {																-- date format is dMy-dMy; reformat to:
 		['dmy'] = {'%s %s %s – %s %s %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- for long/short reformatting
 		['mdy'] = {'%s %s, %s – %s %s, %s', 'm', 'd', 'y', 'm2', 'd2', 'y2'},	-- |df=mdy -&gt; Mdy-Mdy 
 		},
 	['Mdy-Mdy'] = {																-- date format is Mdy-Mdy; reformat to:
 		['mdy'] = {'%s %s, %s – %s %s, %s', 'm', 'd', 'y', 'm2', 'd2', 'y2'},	-- for long/short reformatting
 		['dmy'] = {'%s %s %s – %s %s %s', 'd', 'm', 'y', 'd2', 'm2', 'y2'},		-- |df=dmy -&gt; dMy-dMy 
 		},
 	['My-My'] = {																-- these for long/short reformatting
 		['any'] = {'%s %s – %s %s', 'm', 'y', 'm2', 'y2'},						-- dmy/mdy agnostic
 		},
 	['M-My'] = {																-- these for long/short reformatting
 		['any'] = {'%s–%s %s', 'm', 'm2', 'y'},									-- dmy/mdy agnostic
 		},
 	['My'] = {																	-- these for long/short reformatting
 		['any'] = {'%s %s', 'm', 'y'},											-- dmy/mdy agnostic
 		},
 	--	['yMd'] = {																-- not supported at en.wiki
 	--		['mdy'] = {'%s %s, %s', 'm', 'd', 'y'},								-- |df=mdy
 	--		['dmy'] = {'%s %s %s', 'd', 'm', 'y'},								-- |df=dmy
 	--		['ymd'] = {'%s-%s-%s', 'y', 'm', 'd'},								-- |df=ymd
 	--		},
 	}
 
 
 local function reformatter (date, pattern_idx, format_param, mon_len)
 	if not in_array (pattern_idx, {'ymd', 'Mdy', 'Md-dy', 'dMy', 'yMd', 'd-dMy', 'dM-dMy', 'Md-Mdy', 'dMy-dMy', 'Mdy-Mdy', 'My-My', 'M-My', 'My'}) then
 		return;																	-- not in this set of date format patterns then not a reformattable date
 	end
 	
 	if 'ymd' == format_param and in_array (pattern_idx, {'ymd', 'Md-dy', 'd-dMy', 'dM-dMy', 'Md-Mdy', 'dMy-dMy', 'Mdy-Mdy', 'My-My', 'M-My', 'My'}) then
 		return;																	-- ymd date ranges not supported at en.wiki; no point in reformatting ymd to ymd
 	end
 
 	if in_array (pattern_idx, {'My', 'M-My', 'My-My'}) then						-- these are not dmy/mdy so can't be 'reformatted' into either
 		format_param = 'any';													-- so format-agnostic 
 	end
 
 																				-- yMd is not supported at en.wiki; when yMd is supported at your wiki, uncomment the next line
 	--	if 'yMd' == format_param and in_array (pattern_idx, {'yMd', 'Md-dy', 'd-dMy', 'dM-dMy', 'Md-Mdy', 'dMy-dMy', 'Mdy-Mdy'}) then	-- these formats not convertable; yMd not supported at en.wiki
 	if 'yMd' == format_param then												-- yMd not supported at en.wiki; when yMd is supported at your wiki, remove or comment-out this line
 		return;																	-- not a reformattable date
 	end
 	
 	local c1, c2, c3, c4, c5, c6, c7;											-- these hold the captures specified in patterns[pattern_idx][1]
 	c1, c2, c3, c4, c5, c6, c7 = mw.ustring.match (date, patterns[pattern_idx][1]);	-- get the captures
 
 	local t = {																	-- table that holds k/v pairs of date parts from the captures and patterns[pattern_idx][2..]
 		[patterns[pattern_idx][2]] = c1;										-- at minimum there is always one capture with a matching indicator letter
 		[patterns[pattern_idx][3] or 'x'] = c2;									-- patterns can have a variable number of captures; each capture requires an indicator letter;
 		[patterns[pattern_idx][4] or 'x'] = c3;									-- where there is no capture, there is no indicator letter so n in patterns[pattern_idx][n] will be nil;
 		[patterns[pattern_idx][5] or 'x'] = c4;									-- the 'x' here spoofs an indicator letter to prevent 'table index is nil' error
 		[patterns[pattern_idx][6] or 'x'] = c5;
 		[patterns[pattern_idx][7] or 'x'] = c6;
 		[patterns[pattern_idx][8] or 'x'] = c7;
 		};
 
 	if t.a then																	-- if this date has an anchor year capture (all convertable date formats except ymd)
 		if t.y2 then															-- for year range date formats														
 			t.y2 = t.a;															-- use the anchor year capture when reassembling the date
 		else																	-- here for single date formats (except ymd)
 			t.y = t.a;															-- use the anchor year capture when reassembling the date
 		end
 	end
 
 	if tonumber(t.m) then														-- if raw month is a number (converting from ymd)
 		if 's' == mon_len then													-- if we are to use abbreviated month names
 			t.m = cfg.date_names['inv_local_short'][tonumber(t.m)];					-- convert it to a month name
 		else
 			t.m = cfg.date_names['inv_local_long'][tonumber(t.m)];					-- convert it to a month name
 		end
 		t.d = t.d:gsub ('0(%d)', '%1');											-- strip leading '0' from day if present
 	elseif 'ymd' == format_param then											-- when converting to ymd
 		t.y = t.y:gsub ('%a', '');												-- strip CITREF disambiguator if present; anchor year already known so process can proceed; TODO: maint message?
 		if 1582 &gt; tonumber (t.y) then											-- ymd format dates not allowed before 1582
 			return;
 		end
 		t.m = string.format ('%02d', get_month_number (t.m));					-- make sure that month and day are two digits
 		t.d = string.format ('%02d', t.d);
 	elseif mon_len then															-- if mon_len is set to either 'short' or 'long'
 		for _, mon in ipairs ({'m', 'm2'}) do									-- because there can be two month names, check both 
 			if t[mon] then
 				t[mon] = get_month_number (t[mon]);								-- get the month number for this month (is length agnostic)
 				if 0 == t[mon] then return; end									-- seasons and named dates can't be converted
 				t[mon] = (('s' == mon_len) and cfg.date_names['inv_local_short'][t[mon]]) or cfg.date_names['inv_local_long'][t[mon]];	-- fetch month name according to length
 			end
 		end
 	end
 
 	local new_date = string.format (re_formats[pattern_idx][format_param][1],	-- format string
 		t[re_formats[pattern_idx][format_param][2]],							-- named captures from t{}
 		t[re_formats[pattern_idx][format_param][3]],
 		t[re_formats[pattern_idx][format_param][4]],
 		t[re_formats[pattern_idx][format_param][5]],
 		t[re_formats[pattern_idx][format_param][6]],
 		t[re_formats[pattern_idx][format_param][7]],
 		t[re_formats[pattern_idx][format_param][8]]
 		);
 
 	return new_date;
 end
 
 
 --[[-------------------------&lt; R E F O R M A T _ D A T E S &gt;--------------------------------------------------
 
 Reformats existing dates into the format specified by format.
 
 format is one of several manual keywords: dmy, dmy-all, mdy, mdy-all, ymd, ymd-all.  The -all version includes
 access- and archive-dates; otherwise these dates are not reformatted.
 
 This function allows automatic date formatting.  In ~/Configuration, the article source is searched for one of
 the {{use xxx dates}} templates.  If found, xxx becomes the global date format as xxx-all.  If |cs1-dates= in
 {{use xxx dates}} has legitimate value then that value determines how cs1|2 dates will be rendered.  Legitimate
 values for |cs1-dates= are:
 	l - all dates are rendered with long month names
 	ls - publication dates use long month names; access-/archive-dates use abbreviated month names
 	ly - publication dates use long month names; access-/archive-dates rendered in ymd format
 	s - all dates are rendered with abbreviated (short) month names
 	sy - publication dates use abbreviated month names; access-/archive-dates rendered in ymd format
 	y - all dates are rendered in ymd format
 
 the format argument for automatic date formatting will be the format specified by {{use xxx dates}} with the
 value supplied by |cs1-dates so one of: xxx-l, xxx-ls, xxx-ly, xxx-s, xxx-sy, xxx-y, or simply xxx (|cs1-dates=
 empty, omitted, or invalid) where xxx shall be either of dmy or mdy.
 
 dates are extracted from date_parameters_list, reformatted (if appropriate), and then written back into the
 list in the new format.  Dates in date_parameters_list are presumed here to be valid (no errors).  This function
 returns true when a date has been reformatted, false else.  Actual reformatting is done by reformatter().
 
 ]]
 
 local function reformat_dates (date_parameters_list, format)
 	local all = false;															-- set to false to skip access- and archive-dates
 	local len_p = 'l';															-- default publication date length shall be long
 	local len_a = 'l';															-- default access-/archive-date length shall be long
 	local result = false;
 	local new_date;																
 	
 	if format:match('%a+%-all') then											-- manual df keyword; auto df keyword when length not specified in {{use xxx dates}}; 
 		format = format:match('(%a+)%-all');									-- extract the format
 		all = true;																-- all dates are long format dates because this keyword doesn't specify length
 	elseif format:match('%a+%-[lsy][sy]?') then									-- auto df keywords; internal only
 		all = true;																-- auto df applies to all dates; use length specified by capture len_p for all dates
 		format, len_p, len_a = format:match('(%a+)%-([lsy])([sy]?)');			-- extract the format and length keywords
 		if 'y' == len_p then													-- because allowed by MOS:DATEUNIFY (sort of) range dates and My dates not reformatted
 			format = 'ymd';														-- override {{use xxx dates}}
 		elseif (not is_set(len_a)) or (len_p == len_a) then						-- no access-/archive-date length specified or same length as publication dates then
 			len_a = len_p;														-- in case len_a not set
 		end
 	end																			-- else only publication dates and they are long
 
 	for param_name, param_val in pairs (date_parameters_list) do				-- for each date-holding parameter in the list
 		if is_set (param_val.val) then											-- if the parameter has a value
 			if not (not all and in_array (param_name, {'access-date', 'archive-date'})) then	-- skip access- or archive-date unless format is xxx-all; yeah, ugly; TODO: find a better way
 				for pattern_idx, pattern in pairs (patterns) do
 					if mw.ustring.match (param_val.val, pattern[1]) then
 						if all and in_array (param_name, {'access-date', 'archive-date'}) then	-- if this date is an access- or archive-date
 							new_date = reformatter (param_val.val, pattern_idx, (('y' == len_a) and 'ymd') or format, len_a);	-- choose ymd or dmy/mdy according to len_a setting
 						else													-- all other dates
 							new_date = reformatter (param_val.val, pattern_idx, format, len_p);
 						end
 						
 						if new_date then										-- set when date was reformatted
 							date_parameters_list[param_name].val = new_date;	-- update date in date list
 							result = true;										-- and announce that changes have been made
 							break;
 						end
 					end	-- if
 				end		-- for
 			end			-- if
 		end				-- if
 	end					-- for
 	return result;																-- declare boolean result and done
 end
 
 
 --[[--------------------------&lt; D A T E _ H Y P H E N _ T O _ D A S H &gt;----------------------------------------
 
 Loops through the list of date-holding parameters and converts any hyphen to an ndash.  Not called if the cs1|2
 template has any date errors.
 
 Modifies the date_parameters_list and returns true if hyphens are replaced, else returns false.
 
 ]]
 
 local function date_hyphen_to_dash (date_parameters_list)
 	local result = false;
 	local n;
 	for param_name, param_val in pairs(date_parameters_list) do					-- for each date-holding parameter in the list
 		if is_set (param_val.val) and
 			not mw.ustring.match (param_val.val, patterns.ymd[1]) then			-- for those that are not ymd dates (ustring because here digits may not be Western)
 				param_val.val, n = param_val.val:gsub ('%-', '–');				-- replace any hyphen with ndash
 				if 0 ~= n then
 					date_parameters_list[param_name].val = param_val.val;		-- update the list
 					result = true;
 				end
 		end
 	end
 	return result;																-- so we know if any hyphens were replaced
 end
 
 
 --[[-------------------------&lt; D A T E _ N A M E _ X L A T E &gt;------------------------------------------------
 
 Attempts to translate English date names to local-language date names using names supplied by MediaWiki's
 date parser function.  This is simple name-for-name replacement and may not work for all languages.
 
 if xlat_dig is true, this function will also translate Western (English) digits to the local language's digits.
 This will also translate ymd dates.
 
 ]]
 
 local function date_name_xlate (date_parameters_list, xlt_dig)
 	local xlate;
 	local mode;																	-- long or short month names
 	local modified = false;
 	local date;
 	
 	local sources_t = {
 		{cfg.date_names.en.long, cfg.date_names.inv_local_long},				-- for translating long English month names to long local month names
 		{cfg.date_names.en.short, cfg.date_names.inv_local_short},				-- short month names
 		{cfg.date_names.en.quarter, cfg.date_names.inv_local_quarter},			-- quarter date names
 		{cfg.date_names.en.season, cfg.date_names.inv_local_season},			-- season date nam
 		{cfg.date_names.en.named, cfg.date_names.inv_local_named},				-- named dates
 		}
 
 	local function is_xlateable (month)											-- local function to get local date name that replaces existing English-language date name
 		for _, date_names_t in ipairs (sources_t) do							-- for each sequence table in date_names_t
 			if date_names_t[1][month] then										-- if date name is English month (long or short), quarter, season or named and
 				if date_names_t[2][date_names_t[1][month]] then					-- if there is a matching local date name
 					return date_names_t[2][date_names_t[1][month]];				-- return the local date name
 				end
 			end
 		end
 	end
 
 	for param_name, param_val in pairs(date_parameters_list) do					-- for each date-holding parameter in the list
 		if is_set(param_val.val) then											-- if the parameter has a value
 			date = param_val.val;
 			for month in mw.ustring.gmatch (date, '[%a ]+') do					-- iterate through all date names in the date (single date or date range)
 				month = mw.text.trim (month);									-- this because quarterly dates contain whitespace
 				xlate = is_xlateable (month);									-- get translate &lt;month&gt;; returns translation or nil
 				
 				if xlate then		
 					date = mw.ustring.gsub (date, month, xlate);				-- replace the English with the translation
 					date_parameters_list[param_name].val = date;				-- save the translated date
 					modified = true;
 				end
 			end
 
 			if xlt_dig then														-- shall we also translate digits?
 				date = date:gsub ('%d', cfg.date_names.xlate_digits);			-- translate digits from Western to 'local digits'
 				date_parameters_list[param_name].val = date;					-- save the translated date
 				modified = true;
 			end
 		end
 	end
 	
 	return modified;
 end
 
 
 --[[--------------------------&lt; S E T _ S E L E C T E D _ M O D U L E S &gt;--------------------------------------
 
 Sets local imported functions table to same (live or sandbox) as that used by the other modules.
 
 ]]
 
 local function set_selected_modules (cfg_table_ptr, utilities_page_ptr)
 	add_prop_cat = utilities_page_ptr.add_prop_cat ;							-- import functions from selected Module:Citation/CS1/Utilities module
 	is_set = utilities_page_ptr.is_set;
 	in_array = utilities_page_ptr.in_array;
 	set_message = utilities_page_ptr.set_message;
 	substitute = utilities_page_ptr.substitute;
 	wrap_style = utilities_page_ptr.wrap_style;
 
 	cfg = cfg_table_ptr;														-- import tables from selected Module:Citation/CS1/Configuration
 end
 
 
 --[[--------------------------&lt; A R C H I V E _ D A T E _ C H E C K &gt;------------------------------------------
 
 Compare value in |archive-date= with the timestamp in Wayback machine urls.  Emits an error message when |archive-date=
 does not match the timestamp.
 
 ]]
 
 local function archive_date_check (archive_date, archive_url_timestamp)
 	local good, archive_date_ts = pcall (lang_object.formatDate, lang_object, 'Ymd', archive_date);		-- |archive-date= value to YYYYMMDD format
 --	local archive_date_ts = lang_object:formatDate ('Ymd', archive_date);		-- |archive-date= value to YYYYMMDD format
 
 	if good then
 		if not archive_url_timestamp:find (archive_date_ts, 1, true) then		-- plain text find; begin search at position 1
 			set_message ('err_archive_date_url_ts_mismatch');					-- emit an error message
 		end
 	end
 end
 
 
 --[[--------------------------&lt; E X P O R T E D   F U N C T I O N S &gt;------------------------------------------
 ]]
 
 return {																		-- return exported functions
 	archive_date_check = archive_date_check,
 	date_hyphen_to_dash = date_hyphen_to_dash,
 	date_name_xlate = date_name_xlate,
 	dates = dates,
 	reformat_dates = reformat_dates,
 	set_selected_modules = set_selected_modules,
 	year_date_check = year_date_check,