day, day2, month, anchor_year, year = mw.ustring.match(date_string, patterns['d-dMy'][1]);
if tonumber(day) >= tonumber(day2) then return false; end -- date range order is to : 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 to : 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) <= tonumber(year) then return false; end -- must be sequential years, to , 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) <= tonumber(year) then return false; end -- must be sequential years, to , 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, to , 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); -- <month> 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, to , 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) >= tonumber(year2) then return false; end -- to , 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) >= tonumber(year2) then return false; end -- to , 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 in_array (param, {'date', 'publication-date', 'year'}) then
add_prop_cat ('year-range-abbreviated');
end  
if 13 > 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) >= tonumber(year2) then return false; end -- to , 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['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