䀡碼源𧵑模庉:Category series navigation

require('strict')
local p = {}
local horizontal = require('Module:List').horizontal

--[[==========================================================================]]
--[[                                Globals                                   ]]
--[[==========================================================================]]

local currtitle = mw.title.getCurrentTitle()
local nexistingcats = 0
local errors = ''
local testcasecolon = ''
local testcases = string.match(currtitle.subpageText, '^testcases')
if    testcases then testcasecolon = ':' end
local navborder = true
local followRs = true
local skipgaps = false
local skipgaps_limit = 50
local term_limit = 10
local hgap_limit = 6
local ygap_limit = 5
local listall = false
local tlistall = {}
local tlistallbwd = {}
local tlistallfwd = {}
local ttrackingcats = { --when reindexing, Ctrl+H 'trackcat(13,' & 'ttrackingcats[16]'
	'', -- [1] placeholder for [[Thể loại:Category series navigation using cat parameter]]
	'', -- [2] placeholder for [[Thể loại:Category series navigation using testcase parameter]]
	'', -- [3] placeholder for [[Thể loại:Category series navigation using unknown parameter]]
	'', -- [4] placeholder for [[Thể loại:Category series navigation range not using en dash]]
	'', -- [5] placeholder for [[Thể loại:Category series navigation range abbreviated (CNBS)]]
	'', -- [6] placeholder for [[Thể loại:Category series navigation range redirected (base change)]]
	'', -- [7] placeholder for [[Thể loại:Category series navigation range redirected (var change)]]
	'', -- [8] placeholder for [[Thể loại:Category series navigation range redirected (end)]]
	'', -- [9] placeholder for [[Thể loại:Category series navigation range redirected (CNBS)]]
	'', --[10] placeholder for [[Thể loại:Category series navigation range redirected (other)]]
	'', --[11] placeholder for [[Thể loại:Category series navigation range gaps]]
	'', --[12] placeholder for [[Thể loại:Category series navigation range irregular]]
	'', --[13] placeholder for [[Thể loại:Category series navigation range irregular, 0-length]]
	'', --[14] placeholder for [[Thể loại:Category series navigation range ends (present)]]
	'', --[15] placeholder for [[Thể loại:Category series navigation range ends (blank, CNBS)]]
	'', --[16] placeholder for [[Thể loại:Category series navigation isolated]]
	'', --[17] placeholder for [[Thể loại:Category series navigation default season gap size]]
	'', --[18] placeholder for [[Thể loại:Category series navigation decade redirected]]
	'', --[19] placeholder for [[Thể loại:Category series navigation year redirected (base change)]]
	'', --[20] placeholder for [[Thể loại:Category series navigation year redirected (var change)]]
	'', --[21] placeholder for [[Thể loại:Category series navigation year redirected (other)]]
	'', --[22] placeholder for [[Thể loại:Category series navigation roman numeral redirected]]
	'', --[23] placeholder for [[Thể loại:Category series navigation nordinal redirected]]
	'', --[24] placeholder for [[Thể loại:Category series navigation wordinal redirected]]
	'', --[25] placeholder for [[Thể loại:Category series navigation TV season redirected]]
	'', --[26] placeholder for [[Thể loại:Category series navigation using skip-gaps parameter]]
	'', --[27] placeholder for [[Thể loại:Category series navigation year and range]]
	'', --[28] placeholder for [[Thể loại:Category series navigation year and decade]]
	'', --[29] placeholder for [[Thể loại:Category series navigation decade and century]]
	'', --[30] placeholder for [[Thể loại:Category series navigation in mainspace]]
	'', --[31] placeholder for [[Thể loại:Category series navigation redirection error]]
}
local avoidself =  (not string.match(currtitle.text, 'Category series navigation with') and
					not string.match(currtitle.text, 'Category series navigation.*/doc') and
					not string.match(currtitle.text, 'Category series navigation.*/sandbox') and
					currtitle.text ~= 'Category series navigation' and
					currtitle.nsText:gsub('_', ' ') ~= 'Thảo luận Thành viên' and -- [[phab:T369784]]
					currtitle.nsText:gsub('_', ' ') ~= 'Thảo luận Bản mẫu' and
					(currtitle.nsText ~= 'Bản_mẫu' or testcases)) --avoid nested transclusion errors (i.e. {{Infilmdecade}})


--[[==========================================================================]]
--[[                      Utility & category functions                        ]]
--[[==========================================================================]]

--Determine if a category exists (in a function for easier localization).
local function catexists( title )
	return mw.title.new( title, 'Thể_loại' ).exists
end

--Error message handling.
function p.errorclass( msg )
	return mw.text.tag( 'span', {class='error mw-ext-cite-error'}, '<b>Lỗi!</b> '..string.gsub(msg, '&#', '&amp;#') )
end

--Failure handling.
function p.failedcat( errors, sortkey )
	if avoidself then
		return (errors or '')..'&#42;&#42;&#42;Category series navigation tạo navbox không thành công***'..
			   '[['..testcasecolon..'Thể loại:Category series navigation tạo navbox không thành công|'..(sortkey or 'O')..']]\n'
	end
	return ''
end

--Tracking cat handling.
--	key: 15 (when reindexing ttrackingcats{}, Ctrl+H 'trackcat(13,' & 'ttrackingcats[16]')
--	cat: 'Category series navigation isolated'; '' to remove
--Used by main, all nav_*(), & several utility functions.
local function trackcat( key, cat )
	if avoidself and key and cat then
		if cat ~= '' then
			ttrackingcats[key] = '[['..testcasecolon..'Thể loại:'..cat..']]'
		else
			ttrackingcats[key] = ''
		end
	end
	return
end

--Check for unknown parameters.
--Used by main only.
local function checkforunknownparams( tbl )
	local knownparams = { --parameter whitelist
		['min'] = 'min',
		['max'] = 'max',
		['cat'] = 'cat',
		['show'] = 'show',
		['testcase'] = 'testcase',
		['testcasegap'] = 'testcasegap',
		['skip-gaps'] = 'skip-gaps',
		['list-all-links'] = 'list-all-links',
		['follow-redirects'] = 'follow-redirects',
	}
	for k, _ in pairs (tbl) do
		if knownparams[k] == nil then
			trackcat(3, 'Category series navigation sử dụng tham số không rõ')
			break
		end
	end
end

--Check for nav_*() navigational isolation (not necessarily an error).
--Used by all nav_*().
local function isolatedcat()
	if nexistingcats == 0 then
		trackcat(16, 'Category series navigation cô lập')
	end
end

--Returns the target of {{Đổi hướng thể loại}}, if it exists, else returns the original cat.
--{{Title year}}, etc., if found, are evaluated.
--Used by catlinkfollowr(), and so indirectly by all nav_*().
local function rtarget( frame, cat )
	local catcontent = mw.title.new( cat or '', 'Thể_loại' ):getContent()
	if string.match( catcontent or '', '{{ *[Đ]ổi' ) then --prelim test
		local getRegex = require('Module:Template redirect regex').main
		local tregex = getRegex('Đổi hướng thể loại')
		for _, v in pairs (tregex) do
			local rtarget = mw.ustring.match( catcontent, v..'%s*|%s*([^|}]+)' )
			if rtarget then
				if string.match(rtarget, '{{') then --{{Title year}}, etc., exists; evaluate
					local regex_ty = '%s*|%s*([^{}]*{{([^{|}]+)}}[^{}]-)%s*}}' --eval null-param templates only; expanded if/as needed
					local rtarget_orig, ty = mw.ustring.match( catcontent, v..regex_ty )
					if rtarget_orig then
						local ty_eval = frame:expandTemplate{ title = ty, args = { page = cat } } --frame:newChild doesn't work, use 'page' param instead
						local rtarget_eval = mw.ustring.gsub(rtarget_orig, '{{%s*'..ty..'%s*}}', ty_eval )
						return rtarget_eval
					else --sub-parameters present; track & return default
						trackcat(31, 'Category series navigation có lỗi đổi hướng')
					end
				end
				rtarget = mw.ustring.gsub(rtarget, '^1%s*=%s*', '')
				rtarget = string.gsub(rtarget, '^[Tt]hể loại:', '')
				return rtarget
			end
		end --for
	end --if
	return cat
end

--Similar to {{LinkCatIfExists2}}: make a piped link to a category, if it exists;
--if it doesn't exist, just display the greyed link title without linking.
--Follows {{Đổi hướng thể loại}}s.
--Returns {
--			['cat'] = cat,
--			['catexists'] = true,
--			['rtarget'] = <#R target>,
--			['navelement'] = <#R target navelement>,
--			['displaytext'] = displaytext,
--		  }
--		  if #R followed;
--returns {
--			['cat'] = cat,
--			['catexists'] = <true|false>,
--			['rtarget'] = nil,
--			['navelement'] = <cat navelement>,
--			['displaytext'] = displaytext,
--		  }
--		  otherwise.
--Used by all nav_*().
local function catlinkfollowr( frame, cat, displaytext, displayend, listoverride )
	cat         = mw.text.trim(cat or '')
	displaytext = mw.text.trim(displaytext or '')
	displayend  = displayend or false --bool flag to override displaytext IIF the cat/target is terminal (e.g. "2021–present" or "2021–")
	
	local disp = cat
	if displaytext ~= '' then --use 'displaytext' parameter if present
		disp = mw.ustring.gsub(displaytext, '%s+%(.+$', ''); --strip any trailing disambiguator
	end
	
	local link, nilorR
	local exists = catexists(cat)
	if exists then
		nexistingcats = nexistingcats + 1
		if followRs then
			local R = rtarget(frame, cat) --find & follow #R
			if R ~= cat then --#R followed
				nilorR = R
			end
			
			if displayend then
				local y, hyph, ending = mw.ustring.match(R, '^.-(%d+)([–-])(.*)$')
				if ending == 'nay' then
					disp = y..hyph..ending
				elseif ending == '' then
					disp = y..hyph..'<span style="visibility:hidden">'..y..'</span>' --hidden y to match spacing
				end
			end
			
			link = '[[:Thể loại:'..R..'|'..disp..']]'
		else
			link = '[[:Thể loại:'..cat..'|'..disp..']]'
		end
	else
		link = '<span class="categorySeriesNavigation-item-inactive">'..disp..'</span>'
	end
	
	if listall and listoverride == nil then
		if nilorR then --#R followed
			table.insert( tlistall, '[[:Thể loại:'..cat..']] → '..'[[:Thể loại:'..nilorR..']] ('..link..')' )
		else --no #R
			table.insert( tlistall, '[[:Thể loại:'..cat..']] ('..link..')' )
		end
	end
	
	return {
		['cat'] = cat,
		['catexists'] = exists,
		['rtarget'] = nilorR,
		['navelement'] = link,
		['displaytext'] = disp,
	}
end

--Returns a numbered list of all {{Đổi hướng thể loại}}s followed by catlinkfollowr() -> rtarget().
--For a nav_hyphen() cat, also returns a formatted list of all cats searched for & found, & all loop indices.
--Used by all nav_*().
local function listalllinks()
	local nl = '\n# '
	local out = ''
	if currtitle.nsText == 'Thể_loại' then
		errors = p.errorclass('Tham số/công cụ <b><code>|list-all-links=yes</code></b> '..
							'không nên được lưu trong không gian thể loại, mà chỉ có thể xem trước.')
		out = p.failedcat(errors, 'Z')
	end
	
	local bwd, fwd = '', ''
	if tlistallbwd[1] then
		bwd = '\n\nbackward search:'..nl..table.concat(tlistallbwd, nl)
	end
	if tlistallfwd[1] then
		fwd = '\n\nforward search:'..nl..table.concat(tlistallfwd, nl)
	end
	
	if tlistall[1] then
		return out..nl..table.concat(tlistall, nl)..bwd..fwd
	else
		return out..nl..'Không tìm thấy liên kết!?'..bwd..fwd
	end
end

--Returns the difference b/w 2 ints separated by endash|hyphen, nil if error.
--Used by nav_hyphen() only.
local function find_duration( cat )
	local from, to = mw.ustring.match(cat, '(%d+)[–-](%d+)')
	if from and to then
		if to == '00' then return nil end --doesn't follow CNBS:DATERANGE
		if (#from == 4) and (#to == 2) then             --1900-01
			to = string.match(from, '(%d%d)%d%d')..to   --1900-1901
		elseif (#from == 2) and (#to == 4) then         --  01-1902
			from = string.match(to, '(%d%d)%d%d')..from --1901-1902
		end
		return (tonumber(to) - tonumber(from))
	end
	return 0
end

--Returns the ending of a terminal cat, and sets the appropriate tracking cat, else nil.
--Used by nav_hyphen() only.
local function find_terminaltxt( cat )
	local terminaltxt = nil
	if mw.ustring.match(cat, '%d+[–-]nay$') then
		terminaltxt = 'nay'
		trackcat(14, 'Category series navigation có khoảng kết thúc (hiện tại)')
	elseif mw.ustring.match(cat, '%d+[–-]$') then
		terminaltxt = ''
		trackcat(15, 'Category series navigation có khoảng kết thúc (trắng, CNBS)')
	end
	return terminaltxt
end

--Returns an unsigned string of the 1-4 digit decade ending in "0", else nil.
--Used by nav_decade() only.
local function sterilizedec( decade )
	if decade == nil or decade == '' then
		return nil
	end
	
	local dec = string.match(decade, '^[-%+]?(%d?%d?%d?0)$') or
				string.match(decade, '^[-%+]?(%d?%d?%d?0)%D')
	if dec then
		return dec
	else
		--fix 2-4 digit decade
		local decade_fixed234 = string.match(decade, '^[-%+]?(%d%d?%d?)%d$') or
								string.match(decade, '^[-%+]?(%d%d?%d?)%d%D')
		if decade_fixed234 then
			return decade_fixed234..'0'
		end
		
		--fix 1-digit decade
		local decade_fixed1   = string.match(decade, '^[-%+]?(%d)$') or
								string.match(decade, '^[-%+]?(%d)%D')
		if decade_fixed1 then
			return '0'
		end
		
		--unfixable
		return nil
	end
end

--Check for nav_hyphen default gap size + isolatedcat() (not necessarily an error).
--Used by nav_hyphen() only.
local function defaultgapcat( bool )
	if bool and nexistingcats == 0 then
		--using "nexistingcats > 0" isn't as useful, since the default gap size obviously worked
		trackcat(17, 'Category series navigation có khoảng cách thời gian mặc định')
	end
end

--12 -> 12th, etc.
--Used by nav_nordinal() & nav_wordinal().
function p.addord( i )
	if tonumber(i) then
		local s = tostring(i)
		
		local tens = string.match(s, '1%d$')
		if    tens then return s end
		
		local  ones = string.match(s, '%d$')
		if     ones == '1' then return s
		elseif ones == '2' then return s
		elseif ones == '3' then return s end
		
		return s
	end
	return i
end

--Returns the properly formatted central nav element.
--Expects an integer i, and a catlinkfollowr() table.
--Used by nav_decade() & nav_ordinal() only.
local function navcenter( i, catlink )
	if i == 0 then --center nav element
		if navborder == true then
			return '<b>'..catlink.displaytext..'</b>'
		else
			return '<b>'..catlink.navelement..'</b>'
		end
	else
		return catlink.navelement
	end
end

--Wrap one or two navs in a <div> with ARIA attributes; add TemplateStyles
--before it. This also aligns the navs in case some floating element (like a
--portal box) breaks their alignment.
--Used by main only.
local function wrap( nav1, nav2 )
	local templatestyles = require("Module:TemplateStyles")(
		"Module:Category series navigation/styles.css"
	)
	local prepare = function (nav)
		if nav then
			nav = '\n'..nav
		else
			nav = ''
		end
		return nav
	end
	return templatestyles..
		'<div class="categorySeriesNavigation" role="navigation" aria-label="Range">'..
		prepare(nav1)..prepare(nav2)..
		'\n</div>'
end


--[[==========================================================================]]
--[[                  Formerly separated templates/modules                    ]]
--[[==========================================================================]]


--[[==========================={{  nav_hyphen  }}=============================]]

local function nav_hyphen( frame, start, hyph, finish, firstpart, lastpart, minseas, maxseas, testgap )
	--Expects a PAGENAME of the form "Some sequential 2015–16 example cat", where
	--	start     = 2015
	--	hyph      = –
	--	finish    = 16 (sequential years can be abbreviated, but others should be full year, e.g. "2001–2005")
	--	firstpart = Some sequential
	--	lastpart  = example cat
	--	minseas   = 1800 ('min' starting season shown; optional; defaults to -9999)
	--	maxseas   = 2000 ('max' starting season shown; optional; defaults to 9999; 2000 will show 2000-01)
	--	testgap   = 0 (testcasegap parameter for easier testing; optional)
	
	--sterilize start
	if string.match(start or '', '^%d%d?%d?%d?$') == nil then --1-4 digits, AD only
		local start_fixed = mw.ustring.match(start or '', '^%s*(%d%d?%d?%d?)%D')
		if start_fixed then
			start = start_fixed
		else
			errors = p.errorclass('Hàm nav_hyphen không thể nhận ra số "'..(start or '')..'" '..
								  'trong phần đầu của tham số "season" được đưa vào nó. '..
								  'V.d. "2015–16", "2015" lẽ ra phải được nhận ra bằng "|2015|–|16|".')
			return p.failedcat(errors, 'H')
		end
	end
	local nstart = tonumber(start)
	
	--en dash check
	if hyph ~= '–' then
		trackcat(4, 'Category series navigation có khoảng không sử dụng en dash') --nav still processable, but track
	end
	
	--sterilize finish & check for weird parents
	local tgaps   = {} --table of gap sizes found b/w terms    { [<gap size found>]    = 1 } for -3 <= j <= 3
	local tgapsj4 = {} --table of gap sizes found b/w terms    { [<gap size found>]    = 1 } for j = { -4, 4 }
	local ttlens  = {} --table of term lengths found w/i terms { [<term length found>] = 1 }
	local tirregs = {} --table of ir/regular-term-length cats' "from"s & "to"s found
	local regularparent = true
	if (finish == -1) or --"Members of the Scottish Parliament 2021–present"
	   (finish == 0)	 --"Members of the Scottish Parliament 2021–"
	then
		regularparent = false
		if maxseas == nil or maxseas == '' then
			maxseas = start --hide subsequent ranges
		end
		if finish == -1 then trackcat(14, 'Category series navigation có khoảng kết thúc (hiện tại)')
		else				 trackcat(15, 'Category series navigation có khoảng kết thúc (trắng, CNBS)') end
	elseif (start == finish) and
		   (ttrackingcats[16] ~= '') --nav_year found isolated; check for surrounding hyphenated terms (e.g. UK MPs 1974)
	then
		trackcat(16, '') --reset for another check later
		trackcat(13, 'Category series navigation có khoảng bất thường, độ dài 0')
		ttlens[0] = 1 --calc ttlens for std cases below
		regularparent = 'isolated'
	end
	if (string.match(finish or '', '^%d+$') == nil) and
	   (string.match(finish or '', '^%-%d+$') == nil)
	then
		local finish_fixed = mw.ustring.match(finish or '', '^%s*(%d%d?%d?%d?)%D')
		if finish_fixed then
			finish = finish_fixed
		else
			errors = p.errorclass('Hàm nav_hyphen không thể nhận ra số "'..(finish or '')..'" '..
								  'trong phần thứ hai của tham số "season" được đưa vào nó. '..
								  'V.d. "2015–16", "16" lẽ ra phải được nhận ra bằng "|2015|–|16|".')
			return p.failedcat(errors, 'I')
		end
	else
		if string.len(finish) >= 5 then
			errors = p.errorclass('Phần thứ hai của tham số season đưa vào hàm nav_hyphen chỉ nên có bốn số hoặc ít hơn, không phải "'..(finish or '')..'". '..
								  'Xem [[CNBS:DATERANGE]] để biết thêm thông tin.')
			return p.failedcat(errors, 'J')
		end
	end
	local nfinish = tonumber(finish)
	
	--save sterilized parent range for easier lookup later
	tirregs['from0'] = nstart
	tirregs['to0']   = nfinish
	
	--sterilize min/max
	local nminseas_default = -9999
	local nmaxseas_default =  9999
	local nminseas = tonumber(minseas) or nminseas_default --same behavior as nav_year
	local nmaxseas = tonumber(maxseas) or nmaxseas_default --same behavior as nav_year
	if nminseas > nstart then nminseas = nstart end
	if nmaxseas < nstart then nmaxseas = nstart end
	
	local lspace = ' ' --assume a leading space (most common)
	local tspace = ' ' --assume a trailing space (most common)
	if string.match(firstpart, '%($') then lspace = '' end --DNE for "Madrid city councillors (2007–2011)"-type cats
	if string.match(lastpart,  '^%)') then tspace = '' end --DNE for "Madrid city councillors (2007–2011)"-type cats
	
	--calculate term length/intRAseason size & finishing year
	local t = 1
	while t <= term_limit and regularparent == true do
		local nish = nstart + t --use switchADBC to flip this sign to work for years BC, if/when the time comes
		if (nish == nfinish) or (string.match(nish, '%d?%d$') == finish) then
			ttlens[t] = 1
			break
		end
		if t == term_limit then
			errors = p.errorclass('Hàm nav_hyphen không thể xác định khoảng định nghĩa phù hợp cho "'..start..hyph..finish..'".')
			return p.failedcat(errors, 'K')
		end
		t = t + 1
	end
	
	--apply CNBS:DATERANGE to parent
	local lenstart = string.len(start)
	local lenfinish = string.len(finish)
	if lenstart == 4 and regularparent == true then --"2001–..."
		if t == 1 then --"2001–02" & "2001–2002" both allowed
			if lenfinish ~= 2 and lenfinish ~= 4 then
				errors = p.errorclass('Phần thứ hai của tham số season đưa vào hàm nav_hyphen nên có hai hoặc bốn số, không phải "'..finish..'".')
				return p.failedcat(errors, 'L')
			end
		else --"2001–2005" is required for t > 1; track "2001–05"; anything else = error
			if lenfinish == 2 then
				trackcat(5, 'Category series navigation có khoảng viết tắt (CNBS)')
			elseif lenfinish ~= 4 then
				errors = p.errorclass('Phần thứ hai của tham số season đưa vào hàm nav_hyphen chỉ nên có bốn số, không phải "'..finish..'".')
				return p.failedcat(errors, 'M')
			end
		end
		if finish == '00' then --full year required regardless of term length
			trackcat(5, 'Category series navigation có khoảng viết tắt (CNBS)')
		end
	end
	
	--calculate intERseason gap size
	local hgap_default     = 0 --assume & start at the most common case: 2001–02 -> 2002–03, etc.
	local hgap_limit_reg   = hgap_limit --less expensive per-increment (inc x 4)
	local hgap_limit_irreg = hgap_limit --more expensive per-increment (inc x 23 = inc x (k_bwd + k_fwd) = inc x (12 + 11))
	local hgap_success = false
	local hgap = hgap_default
	while hgap <= hgap_limit_reg and regularparent == true do --verify
		local prevseason2 = firstpart..lspace..(nstart-t-hgap)..hyph..string.match(nstart-hgap, '%d?%d$')    ..tspace..lastpart
		local nextseason2 = firstpart..lspace..(nstart+t+hgap)..hyph..string.match(nstart+2*t+hgap, '%d?%d$')..tspace..lastpart
		local prevseason4 = firstpart..lspace..(nstart-t-hgap)..hyph..(nstart-hgap)    ..tspace..lastpart
		local nextseason4 = firstpart..lspace..(nstart+t+hgap)..hyph..(nstart+2*t+hgap)..tspace..lastpart
		if t == 1 then --test abbreviated range first, then full range, to be frugal with expensive functions
			if catexists(prevseason2) or --use 'or', in case we're at the edge of the cat structure,
			   catexists(nextseason2) or --or we hit a "–00"/"–2000" situation on one side
			   catexists(prevseason4) or
			   catexists(nextseason4)
			then
				hgap_success = true
				break
			end
		elseif t > 1 then --test full range first, then abbreviated range, to be frugal with expensive functions
			if catexists(prevseason4) or --use 'or', in case we're at the edge of the cat structure,
			   catexists(nextseason4) or --or we hit a "–00"/"–2000" situation on one side
			   catexists(prevseason2) or
			   catexists(nextseason2)
			then
				hgap_success = true
				break
			end
		end
		hgap = hgap + 1
	end
	if hgap_success == false then
		hgap = tonumber(testgap) or hgap_default --tracked via defaultgapcat()
	end
	
	--preliminary scan to determine ir/regular spacing of nearby cats;
	--to limit expensive function calls, CNBS:DATERANGE-violating cats are ignored;
	--an irregular-term-length series should follow "YYYY..hyph..YYYY" throughout
	local jlimit = 4  --4-a-side if all YYYY-YY, 3-a-side if all YYYY-YYYY, with some threshold in between
	if hgap <= hgap_limit_reg then --also to isolate temp vars
		--find # of nav-visible ir/regular-term-length cats
		local bwanchor = nstart       --backward anchor/common year
		local fwanchor = bwanchor + t --forward anchor/common year
		if regularparent == 'isolated' then
			fwanchor = bwanchor
		end
		local spangreen = '[<span style="color:green">j, g, k = ' --used for/when debugging via list-all-links=yes
		local spanblue = '<span style="color:blue">'
		local spanred = ' (<span style="color:red">'
		local span = '</span>'
		local lastg = nil --to check for run-on searches
		local lastk = nil --to check for run-on searches
		local endfound = false --switch used to stop searching forward
		local iirregs = 0 --index of tirregs[] for j < 0, since search starts from parent
		local j = -jlimit --index of tirregs[] for j > 0 & pseudo navh position
		while j <= jlimit do
			
			if j < 0 then --search backward from parent
				local gbreak = false --switch used to break out of g-loop
				local g = 0 --gap size
				while g <= hgap_limit_irreg do
					local k = 0 --term length: 0 = "0-length", 1+ = normal
					while k <= term_limit do
						local from = bwanchor - k - g
						local to   = bwanchor - g
						local full = mw.text.trim( firstpart..lspace..from..hyph..to..tspace..lastpart )
						if k == 0 then
							if regularparent ~= 'isolated' then --+restrict to g == 0 if repeating year problems arise
								to = '0-length'
								full = mw.text.trim( firstpart..lspace..from..tspace..lastpart )
								if catlinkfollowr( frame, full ).rtarget ~= nil then --#R followed
									table.insert( tlistallbwd, spangreen..j..', '..g..', '..k..span..'] '..full..spanred..'#R ignored'..span..')' )
									full, to = '', '' --don't use/follow 0-length cat #Rs from nav_hyphen(); otherwise gets messy
								end
							end
						end
						if (k >= 1) or		  --the normal case; only continue k = 0 if 0-length found
						   (to == '0-length') --ghetto "continue" (thx Lua) to avoid expensive searches for "UK MPs 1974-1974", etc.
						then
							table.insert( tlistallbwd, spangreen..j..', '..g..', '..k..span..'] '..full )
							if (k == 1) and
--							   (g == 0 or g == 1) and --commented to match j>0 case ("1995–96 in Federal Republic of Yugoslavia basketball")
							   (catexists(full) == false)
							then --allow bare-bones CNBS:DATERANGE alternation, in case we're on a 0|1-gap, 1-year term series
								local to2 = string.match(to, '%d%d$')
								if to2 and to2 ~= '00' then --and not at a century transition (i.e. 1999–2000)
									to = to2
									full = mw.text.trim( firstpart..lspace..from..hyph..to..tspace..lastpart )
									table.insert( tlistallbwd, spangreen..j..', '..g..', '..k..span..'] '..full )
								end
							end
							if catexists(full) then
								if to == '0-length' then
									trackcat(13, 'Category series navigation có khoảng bất thường, độ dài 0')
								end
								tlistallbwd[#tlistallbwd] = spanblue..tlistallbwd[#tlistallbwd]..span..' (found)'
								ttlens[ find_duration(full) ] = 1
								if j == -1 then tgapsj4[g] = 1 -- -1 since bwd search starts from parent @ -4 and ends at -1
								else tgaps[g] = 1 end
								iirregs = iirregs + 1
								tirregs['from-'..iirregs] = from
								tirregs['to-'..iirregs] = to
								bwanchor = from --ratchet down
								if to ~= '0-length' then
									gbreak = true
									break
								else
									g = 0 --soft-reset g, to keep stepping thru k
									j = j + 1 --save, but keep searching thru k
									if j > 0 then --(restore "> 3" if acts up) lest we keep searching bwd & finding 0-length cats ("MEPs for the Republic of Ireland 1973" & down)
										j = -1 --allow a normal, full search fwd after break
										gbreak = true
										break
									end
								end
							elseif (j >= 0) and
								   (lastg and lastk) and
								   ((lastg >= hgap_limit_irreg) or
									(lastk >= term_limit))
							then --bwd search exhausted and/or done (runaway bwd search on "2018–19 FIA World Endurance Championship season")
								j = -1 --allow a normal, full search fwd after break
								gbreak = true
								break
							end
						end --ghetto "continue"
						k = k + 1
						lastk = k
					end --while k <= term_limit do
					if gbreak == true then break end
					g = g + 1
					lastg = g
				end --while g <= hgap_limit_irreg do
			end --if j < 0
			
			if j > 0 and endfound == false then --search forward from parent
				local gbreak = false --switch used to break out of g-loop
				local g = 0 --gap size
				while g <= hgap_limit_irreg do
					local k = -2 --term length: -2 = "0-length", -1 = "2020–present", 0 = "2020–", 1+ = normal
					while k <= term_limit do
						local from = fwanchor + g
						local to4  = fwanchor + k + g	--override carefully
						local to2  = nil				--last 2 digits of to4, IIF exists
						if k == -1 then to4 = 'present'	--see if end-cat exists (present)
						elseif k == 0 then to4 = '' end	--see if end-cat exists (blank)
						local full = mw.text.trim( firstpart..lspace..from..hyph..to4..tspace..lastpart )
						if k == -2 then
							if regularparent ~= 'isolated' then --+restrict to g == 0 if repeating year problems arise
								to4 = '0-length' --see if 0-length cat exists
								full = mw.text.trim( firstpart..lspace..from..tspace..lastpart )
								if catlinkfollowr( frame, full ).rtarget ~= nil then --#R followed
									table.insert( tlistallfwd, spangreen..j..', '..g..', '..k..span..'] '..full..spanred..'#R ignored'..span..')' )
									full, to4 = '', '' --don't use/follow 0-length cat #Rs from nav_hyphen(); otherwise gets messy
								end
							end
						end
						if (k >= -1) or		   --only continue k = -2 if 0-length found
						   (to4 == '0-length') --ghetto "continue" (thx Lua) to avoid expensive searches for "UK MPs 1974-1974", etc.
						then
							table.insert( tlistallfwd, spangreen..j..', '..g..', '..k..span..'] '..full )
							if (k == 1) and
--							   (g == 0 or g == 1) and --commented to let "2002–03 in Scottish women's football" find "2008–09 in Scottish women's football"
							   (catexists(full) == false)
							then --allow bare-bones CNBS:DATERANGE alternation, in case we're on a 0|1-gap, 1-year term series
								to2 = string.match(to4, '%d%d$')
								if to2 and to2 ~= '00' then --and not at a century transition (i.e. 1999–2000)
									full = mw.text.trim( firstpart..lspace..from..hyph..to2..tspace..lastpart )
									table.insert( tlistallfwd, spangreen..j..', '..g..', '..k..span..'] '..full )
								end
							end
							if catexists(full) then
								if to4 == '0-length' then
									if rtarget(frame, full) == full then --only use 0-length cats that don't #R
										trackcat(13, 'Category series navigation có khoảng bất thường, độ dài 0')
									end
								end
								tirregs['from'..j] = from
								tirregs['to'..j] = (to2 or to4)
								if (k == -1) or (k == 0) then
									endfound = true --tentative
								else --k == { -2, > 0 }
									tlistallfwd[#tlistallfwd] = spanblue..tlistallfwd[#tlistallfwd]..span..' (found)'
									ttlens[ find_duration(full) ] = 1
									if j == 4 then tgapsj4[g] = 1
									else tgaps[g] = 1 end
									endfound = false
									if to4 ~= '0-length' then --k > 0
										fwanchor = to4 --ratchet up
										gbreak = true
										break --only break on k > 0 b/c old end-cat #Rs still exist like "Members of the Scottish Parliament 2011–"
									else --k == -2
										j = j + 1 --save, but keep searching k's, in case "1974" → "1974-1979"
										if j > jlimit then --lest we keep searching & finding 0-length cats ("2018 CONCACAF Champions League" & up)
											gbreak = true
											break
										elseif g == hgap_limit_irreg then
											--keep searching, since not a runaway, just far away ("American soccer clubs 1958–59 season")
											hgap_limit_irreg = hgap_limit_irreg + 1
										end
									end
								end
							end
						end --ghetto "continue"
						k = k + 1
						lastk = k
					end --while k <= term_limit do
					if gbreak == true then break end
					g = g + 1
					lastg = g
				end --while g <= hgap_limit_irreg do
			end --if j > 0 and endfound == false then
			
			if (lastg and lastk) and
			   (lastg > hgap_limit_irreg) and
			   (lastk > term_limit)
			then --search exhausted
				if j < 0 then j = 0 --bwd search exhausted; continue fwd
				elseif j > 0 then break end --fwd search exhausted
			end
			
			j = j + 1
		end --while j <= jlimit
	end --if hgap <= hgap_limit_reg
	
	--determine # of displayed navh elements based on "YYYY-YY" vs. "YYYY-YYYY" counts
	local Ythreshold = 3.3 --((YYYY-YY x 7) + (YYYY-YYYY x 2))/18 = 3.222; ((YYYY-YY x 6) + (YYYY-YYYY x 3))/18 = 3.333
	local Ycount = 0 --"Y" count
	local ycount = 0 --tirregs counter; # of contiguous #s
	for k, v in pairs (tirregs) do
		local dummy, dunce = mw.ustring.gsub(tostring(v), '%d', '') --why can't gsub just return a table??
		Ycount = Ycount + dunce
		ycount = ycount + 1
	end
	local ycount_limit = ((jlimit * 2) + 1) * 2 --i.e. ((4 * 2) + 1) * 2 = 18
	if ycount < ycount_limit then --fill in the blanks with Ycount_parent, since hidden/dne cats aren't in tirregs
		local dummy_finish = finish
		if not regularparent then dummy_finish = start end
		local dummy, dunce_from = mw.ustring.gsub(start,  '%d', '')
		local dummy, dunce_to   = mw.ustring.gsub(dummy_finish, '%d', '')
		local Ycount_parent_avg = (dunce_from + dunce_to)/2 --"YYYY-YYYY" = 4; "YYYY-YY" = 3
		Ycount = Ycount + (Ycount_parent_avg * (ycount_limit - ycount))
		ycount = ycount_limit
	end
	local iwidth = 3 --default to 3-a-side, 7 total
	local Y_per_y = Ycount / ycount --normalized range: [3-4]
	if Y_per_y < Ythreshold then
		iwidth = 4 --extend to 4-a-side, 9 total
	end
	
	--begin navhyphen
	local navh = '<div class="toccolours categorySeriesNavigation-range">\n'
	
	local navlist = {}
	local terminalcat = false --switch used to hide future cats
	local terminaltxt = nil
	local i = -iwidth --nav position
	while i <= iwidth do
		local from = nstart + i*(t+hgap) --the logical, but not necessarily correct, 'from'
		if tirregs['from'..i] then --prefer the irregular term table
			from = tonumber(tirregs['from'..i])
		else --fallback to lazy/naive 'from'
			if i > 0 and
			   tirregs['from'..(i-1)] and
			   tirregs['from'..(i-1)] >= from
			then --end of the line: avoid dups/past, and create reasonable grey'd ranges
				local greyto   = tonumber(tirregs['to' .. (i-1)]) or -9999
				local greyfrom = tonumber(tirregs['from'..(i-1)]) or -9999
				local grey = greyto --prefer 'to'
				if greyfrom > greyto then grey = greyfrom end --'from' fallback, in case "1995–96", "1995-present", etc.
				if grey > -9999 then
					if grey ~= greyto then
						from = grey + t + hgap --account for missing/incomplete 'to'
					else
						from = grey + hgap
					end
					tirregs['from'..i] = from --remember
					tirregs['to' .. i] = from + t
				end
			elseif i < 0 then
				local greyfrom
				local ii = 0
				while ii < 3 do
					ii = ii + 1
					greyfrom = tonumber(tirregs['from'..(i+ii)])
					if greyfrom then break end
				end
				from = (greyfrom or nstart) - ii*(t+hgap)
				tirregs['from'..i] = from --remember
				tirregs['to' .. i] = from + t
			end
		end
		local from2 = string.match(from, '%d?%d$')
		
		local to = tostring(from+t)	--the logical, naive range, but
		if tirregs['to'..i] then	--prefer irregular term table
			to = tirregs['to'..i]
		elseif regularparent == false and tirregs and i > 0 then
			to = tirregs['to-1']	--special treatment for parent terminal cats, since they have no natural 'to'
		end
		local to2 = string.match(to, '%d?%d$')
		local tofinal = (to2 or '')    --assume t=1 and abbreviated 'to' (the most common case)
		if t > 1 or                    --per CNBS:DATERANGE (e.g. 1999-2004)
		  (from2 - (to2 or from2)) > 0 --century transition exception (e.g. 1999–2000)
		then
			tofinal = (to or '')       --default to the CNBS-correct format, in case no fallbacks found
		end
		if to == '0-length' then
			tofinal = to
		end
		
		--check existance of 4-digit, CNBS-correct range, with abbreviation fallback
		if tofinal ~= '0-length' then
			if t > 1 and string.len(from) == 4 then --e.g. 1999-2004
				--determine which link exists (full or abbr)
				local full = firstpart..lspace..from..hyph..tofinal..tspace..lastpart
				if not catexists(full) then
					local abbr = firstpart..lspace..from..hyph..to2..tspace..lastpart
					if catexists(abbr) then
						tofinal = (to2 or '') --rv to CNBS-incorrect format; if full AND abbr DNE, then tofinal is still in its CNBS-correct format
					end
				end
			elseif t == 1 then --full-year consecutive ranges are also allowed
				local abbr = firstpart..lspace..from..hyph..tofinal..tspace..lastpart --assume tofinal is in abbr format
				if not catexists(abbr) and tofinal ~= to then
					local full = firstpart..lspace..from..hyph..to..tspace..lastpart
					if catexists(full) then
						tofinal = (to or '') --if abbr AND full DNE, then tofinal is still in its abbr format (unless it's a century transition)
		end	end	end	end
		
		--populate navh
		if i ~= 0 then --left/right navh
			local orig = firstpart..lspace..from..hyph..tofinal..tspace..lastpart
			local disp = from..hyph..tofinal
			if tofinal == '0-length' then
				orig = firstpart..lspace..from..tspace..lastpart
				disp = from
			end
			local catlink = catlinkfollowr(frame, orig, disp, true) --force terminal cat display
			
			if terminalcat == false then
				terminaltxt = find_terminaltxt( disp ) --also sets tracking cats
				terminalcat = (terminaltxt ~= nil)
			end
			if catlink.rtarget and avoidself then --a {{Đổi hướng thể loại}} was followed, figure out why
				--determine new term length & gap size
				ttlens[ find_duration( catlink.rtarget ) ] = 1
				if i > -iwidth then
					local lastto = tirregs['to'..(i-1)]
					if lastto == nil then
						local lastfrom = nstart + (i-1)*(t+hgap)
						lastto = lastfrom+t --use last logical 'from' to calc lastto
					end
					if lastto then
						local gapcat = lastto..'-'..from --dummy cat to calc with
						local gap = find_duration(gapcat) or -1	--in case of nil,
						if iwidth == 4 then
							tgapsj4[ gap ] = 1 --tgapsj4[-1] are ignored later
						else
							tgaps[ gap ] = 1 --tgaps[-1] are ignored later
						end
					end
				end
				
				--display/tracking handling
				local base_regex = '%d+[–-]%d+'
				local origbase = mw.ustring.gsub(orig, base_regex, '')
				local rtarbase, rtarbase_success = mw.ustring.gsub(catlink.rtarget, base_regex, '')
				if rtarbase_success == 0 then
					local base_regex_lax = '%d%d%d%d' --in case rtarget is a year cat
					rtarbase, rtarbase_success = mw.ustring.gsub(catlink.rtarget, base_regex_lax, '')
				end
				local terminal_regex = '%d+[–-]'..(terminaltxt or '')..'$' --more manual ORs bc Lua regex sux
				if mw.ustring.match(orig, terminal_regex) then
					origbase = mw.ustring.gsub(orig, terminal_regex, '')
				end
				if mw.ustring.match(catlink.rtarget, terminal_regex) then
					--finagle/overload terminalcat type to set nmaxseas on 1st occurence only
					if terminalcat == false then terminalcat = 1 end
					local dummy = find_terminaltxt( catlink.rtarget ) --also sets tracking cats
					rtarbase = mw.ustring.gsub(catlink.rtarget, terminal_regex, '')
				end
				origbase = mw.text.trim(origbase)
				rtarbase = mw.text.trim(rtarbase)
				if origbase ~= rtarbase then
					trackcat(6, 'Category series navigation có khoảng là đổi hướng (thay đổi gốc)')
				elseif terminalcat == 1 then
					trackcat(8, 'Category series navigation có khoảng là đổi hướng (kết thúc)')
				else --origbase == rtarbase
					local all4s_regex = '%d%d%d%d[–-]%d%d%d%d'
					local orig_all4s = mw.ustring.match(orig, all4s_regex)
					local rtar_all4s = mw.ustring.match(catlink.rtarget, all4s_regex)
					if orig_all4s and rtar_all4s then
						trackcat(10, 'Category series navigation có khoảng là đổi hướng (khác)')
					else
						local year_regex1 = '%d%d%d%d$'
						local year_regex2 = '%d%d%d%d[%s%)]'
						local year_rtar = mw.ustring.match(catlink.rtarget, year_regex1) or
										  mw.ustring.match(catlink.rtarget, year_regex2)
						if orig_all4s and year_rtar then
							trackcat(7, 'Category series navigation có khoảng là đổi hướng (thay đổi var)')
						else
							trackcat(9, 'Category series navigation có khoảng là đổi hướng (CNBS)')
						end
					end
				end
			end
			
			if terminalcat then --true or 1
				if type(terminalcat) ~= 'boolean' then nmaxseas = from end --only want to do this once
				terminalcat = true --done finagling/overloading
			end
			if (from >= 0) and (nminseas <= from) and (from <= nmaxseas) then
				table.insert(navlist, catlink.navelement)
				if terminalcat then nmaxseas = nminseas_default end --prevent display of future ranges
			else
				local hidden = '<span style="visibility:hidden">'..disp..'</span>'
				table.insert(navlist, hidden)
				if listall then
					tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
				end
			end
		else --center navh
			if finish == -1 then finish = 'nay'
			elseif finish == 0 then finish = '<span style="visibility:hidden">'..start..'</span>' end
			local disp = start..hyph..finish
			if regularparent == 'isolated' then disp = start end
			table.insert(navlist, '<b>'..disp..'</b>')
		end
		
		i = i + 1
	end
	
	-- add the list
	navh = navh..horizontal(navlist)..'\n'
	
	--tracking cats & finalize
	if avoidself then
		local igaps  = 0 --# of diff gap sizes > 0 found
		local itlens = 0 --# of diff term lengths found
		for s = 1, hgap_limit_reg do --must loop; #tgaps, #ttlens unreliable
			igaps = igaps + (tgaps[s] or 0)
		end
		if iwidth == 4 then --only count gaps if they were displayed ("Karnataka MLAs 1957–1962")
			for s = 1, hgap_limit_reg do
				igaps = igaps + (tgapsj4[s] or 0)
			end
		end
		for s = 0, term_limit do
			itlens = itlens + (ttlens[s] or 0)
		end
		if igaps  > 0 then trackcat(11, 'Category series navigation có khoảng với chu kỳ') end
		if itlens > 1 and ttrackingcats[13] == '' then --avoid duplication in "Category series navigation range irregular, 0-length"
			trackcat(12, 'Category series navigation có khoảng bất thường')
		end
	end
	isolatedcat()
	defaultgapcat(not hgap_success)
	if listall then
		return listalllinks()
	else
		return navh..'</div>'
	end
end


--[[=========================={{  nav_tvseason  }}============================]]

local function nav_tvseason( frame, firstpart, tv, lastpart, maximumtv )
	--Expects a PAGENAME of the form "Futurama season 1 episodes", where
	--	firstpart = Futurama season
	--	tv        = 1
	--	lastpart  = episodes
	--	maximumtv = 7 ('max' tv season parameter; optional; defaults to 9999)
	tv = tonumber(tv)
	if tv == nil then
		errors = p.errorclass('Hàm nav_tvseason không thể nhận ra số mùa truyền hình được đưa vào tham số thứ 3 của nó.')
		return p.failedcat(errors, 'T')
	end
	
	--"(season 1) episodes" -> "season 1 episodes" following March 2024 RfC:
	--[[Wikipedia talk:Naming conventions (television)#Follow-up RfC on TV season article titles]]
	--                  [[Special:Permalink/1216885280#Follow-up RfC on TV season article titles]]
	local tspace = ' ' --"season 1 episodes"
	local parenth_check = string.match(lastpart, '^%)')
	if parenth_check then tspace = '' end --accommodate old style "(season 1) episodes" just in case
	
	local maxtv_default = 9999
	local maxtv = tonumber(maximumtv) or maxtv_default --allow +/- qualifier
	if maxtv < tv then maxtv = tv end --input error; maxtv should be >= parent
	
	--begin navtvseason
	local navt = '<div class="toccolours categorySeriesNavigation-range">\n'
	
	local navlist = {}
	local prepad = ''
	local i = -5 --nav position
	while i <= 5 do
		local t = tv + i
		if i ~= 0 then --left/right navt
			local catlink = catlinkfollowr( frame, firstpart..' '..t..tspace..lastpart, t )
			if t >= 1 and t <= maxtv then --hardcode mintv
				if catlink.rtarget then --a {{Đổi hướng thể loại}} was followed
					trackcat(25, 'Category series navigation về mùa truyền hình đã đổi hướng')
				end
				if catlink.catexists or
				   (maxtv ~= maxtv_default and t <= maxtv)
				then
					table.insert(navlist, prepad..catlink.navelement) --display normally
					prepad = ''
				else
					local postpad = '<span style="visibility:hidden"> • '..t..'</span>'
					navlist[#navlist] = (navlist[#navlist] or '')..postpad
					if listall then tlistall[#tlistall] = tlistall[#tlistall]..' ('..postpad..')' end
				end	
			elseif t < 1 then
				prepad = prepad..'<span style="visibility:hidden"> • '..'0'..'</span>'
				if listall then tlistall[#tlistall] = (tlistall[#tlistall] or '')..' (x)' end
			else --t > maxtv
				local postpad = '<span style="visibility:hidden"> • '..t..'</span>'
				navlist[#navlist] = navlist[#navlist]..postpad
				if listall then tlistall[#tlistall] = tlistall[#tlistall]..' ('..postpad..')' end
			end
		else --center navt
			table.insert(navlist, prepad..'<b>'..tv..'</b>')
			prepad = ''
		end
		
		i = i + 1
	end
	-- add the list
	navt = navt..horizontal(navlist)..'\n'
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navt..'</div>'
	end
end


--[[==========================={{  nav_decade  }}=============================]]

local function nav_decade( frame, firstpart, decade, lastpart, mindecade, maxdecade )
	--Expects a PAGENAME of the form "Some sequential 2000 example cat", where
	--	firstpart = Some sequential
	--	decade    = 2000
	--	lastpart  = example cat
	--	mindecade = 1800 ('min' decade parameter; optional; defaults to -9999)
	--	maxdecade = 2020 ('max' decade parameter; optional; defaults to 9999)
	
	--sterilize dec
	local dec = sterilizedec(decade)
	if dec == nil then
		errors = p.errorclass('Hàm nav_decade đã được gửi "'..(decade or '')..'" như là tham số thứ 2, '..
							'nhưng nó cần năm từ 1 đến 4 số kết thúc bằng số "0".')
		return p.failedcat(errors, 'D')
	end
	local ndec = tonumber(dec)
	
	--sterilize mindecade & determine AD/BC
	local mindefault = '-9999'
	local mindec = sterilizedec(mindecade) --returns a tostring(unsigned int), or nil
	if mindec then
		if string.match(mindecade, '-%d') or
		   string.match(mindecade, 'TCN')
		then
			mindec = '-'..mindec --better +/-0 behavior with strings (0-initialized int == "-0" string...)
		end
	elseif mindec == nil and mindecade and mindecade ~= '' then
		errors = p.errorclass('Hàm nav_decade đã được gửi "'..(mindecade or '')..'" như là tham số thứ 4, '..
							'nhưng nó cần năm từ 1 đến 4 số kết thúc bằng số "0", chỉ thập niên đầu tiên cần được hiển thị.')
		return p.failedcat(errors, 'E')
	else --mindec == nil
		mindec = mindefault --tonumber() later, after error checks
	end
	
	--sterilize maxdecade & determine AD/BC
	local maxdefault = '9999'
	local maxdec = sterilizedec(maxdecade) --returns a tostring(unsigned int), or nil + error
	if maxdec then
		if string.match(maxdecade, '-%d') or
		   string.match(maxdecade, 'TCN')
		then                     --better +/-0 behavior with strings (0-initialized int == "-0" string...),
			maxdec = '-'..maxdec --but a "-0" string -> tonumber() -> tostring() = "-0",
		end                      --and a  "0" string -> tonumber() -> tostring() =  "0"
	elseif maxdec == nil and maxdecade and maxdecade ~= '' then
		errors = p.errorclass('Hàm nav_decade đã được gửi "'..(maxdecade or '')..'" như là tham số thứ 5, '..
							'nhưng nó cần năm từ 1 đến 4 số kết thúc bằng số "0", chỉ thập niên cuối cùng cần được hiển thị.')
		return p.failedcat(errors, 'F')
	else --maxdec == nil
		maxdec = maxdefault
	end
	
	local tspace = ' ' --assume trailing space for "1950s in X"-type cats
	if string.match(lastpart, '^-') then tspace = '' end --DNE for "1970s-related"-type cats
	
	--AD/BC switches & vars
	
	local parentBC = string.match(lastpart, '^TCN') --following the "0s BC" convention for all years BC
	lastpart = mw.ustring.gsub(lastpart, '^TCN%s*', '') --handle BC separately; AD never used
	--TODO?: handle BCE, but only if it exists in the wild
	
	local dec0to40AD = (ndec >= 0 and ndec <= 40 and not parentBC) --special behavior in this range
	local switchADBC = 1                 --  1=AD parent
	if parentBC then switchADBC = -1 end -- -1=BC parent; possibly adjusted later
	local BCdisp = ''
	local D = -math.huge --secondary switch & iterator for AD/BC transition
	
	--check non-default min/max more carefully
	if mindec ~= mindefault then
		if tonumber(mindec) > ndec*switchADBC then
			mindec = tostring(ndec*switchADBC) --input error; mindec should be <= parent
		end
	end
	if maxdec ~= maxdefault then
		if tonumber(maxdec) < ndec*switchADBC then
			maxdec = tostring(ndec*switchADBC) --input error; maxdec should be >= parent
		end
	end
	local nmindec = tonumber(mindec) --similar behavior to nav_year & nav_nordinal
	local nmaxdec = tonumber(maxdec) --similar behavior to nav_nordinal
	
	--begin navdecade
	local bnb = '' --border/no border
	if navborder == false then --for Category series navigation year and decade
		bnb = 'categorySeriesNavigation-range-transparent'
	end
	local navd = '<div class="toccolours categorySeriesNavigation-range '..bnb..'">\n'
	
	local navlist = {}
	local i = -50 --nav position x 10
	while i <= 50 do
		local d = ndec + i*switchADBC
		
		local BC = ''
		BCdisp = ''
		if dec0to40AD then
			if D < -10 then
				d = math.abs(d + 10) --b/c 2 "0s" decades exist: "0s BC" & "0s" (AD)
				BC = 'TCN '
				if d == 0 then
					D = -10 --track 1st d = 0 use (BC)
				end
			elseif D >= -10 then
				D = D + 10 --now iterate from 0s AD
				d = D      --2nd d = 0 use
			end
		elseif parentBC then
			if switchADBC == -1 then --parentBC looking at the BC side (the common case)
				BC = 'TCN '
				if d == 0 then     --prepare to switch to the AD side on the next iteration
					switchADBC = 1 --1st d = 0 use (BC)
					D = -10        --prep
				end
			elseif switchADBC == 1 then --switched to the AD side
				D = D + 10 --now iterate from 0s AD
				d = D      --2nd d = 0 use (on first use)
			end
		end
		if BC ~= '' and ndec <= 50 then
			BCdisp = ' TCN' --show BC for all BC decades whenever a "0s" is displayed on the nav
		end
		
		--determine target cat
		local disp = 'TN&nbsp;'..d..BCdisp
		local catlink = catlinkfollowr( frame, firstpart..' '..d..tspace..BC..lastpart, disp )
		if catlink.rtarget then --a {{Đổi hướng thể loại}} was followed
			trackcat(18, 'Category series navigation có thập niên đã đổi hướng')
		end
		
		--populate left/right navd
		local shown = navcenter(i, catlink)
		local hidden = '<span style="visibility:hidden">'..disp..'</span>'
		local dsign = d --use d for display & dsign for logic
		if BC ~= '' then dsign = -dsign end
		if (nmindec <= dsign) and (dsign <= nmaxdec) then
			if dsign == 0 and (nmindec == 0 or nmaxdec == 0) then --distinguish b/w -0 (BC) & 0 (AD)
				--"zoom in" on +/- 0 and turn dsign/min/max temporarily into +/- 1 for easier processing
				local zsign, zmin, zmax = 1, nmindec, nmaxdec
				if BC ~= '' then zsign = -1 end
				if     mindec == '-0' then zmin = -1
				elseif mindec ==  '0' then zmin =  1 end
				if     maxdec == '-0' then zmax = -1
				elseif maxdec ==  '0' then zmax =  1 end
				
				if (zmin <= zsign) and (zsign <= zmax) then
					table.insert(navlist, shown)
					hidden = nil
				else
					table.insert(navlist, hidden)
				end
			else
				table.insert(navlist, shown)--the common case
				hidden = nil
			end
		else
			table.insert(navlist, hidden)
		end
		if listall and hidden then
			tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
		end
		
		i = i + 10
	end
	-- add the list
	navd = navd..horizontal(navlist)..'\n'
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navd..'</div>'
	end
end


--[[============================{{  nav_year  }}==============================]]

local function nav_year( frame, firstpart, year, lastpart, minimumyear, maximumyear )
	--Expects a PAGENAME of the form "Some sequential 1760 example cat", where
	--	firstpart   = Some sequential
	--	year        = 1760
	--	lastpart    = example cat
	--	minimumyear = 1758 ('min' year parameter; optional)
	--	maximumyear = 1800 ('max' year parameter; optional)
	local minyear_default = -9999
	local maxyear_default =  9999
	year = tonumber(year) or tonumber(mw.ustring.match(year or '', '^%s*(%d*)'))
	local minyear = tonumber(string.match(minimumyear or '', '-?%d+')) or minyear_default --allow +/- qualifier
	local maxyear = tonumber(string.match(maximumyear or '', '-?%d+')) or maxyear_default --allow +/- qualifier
	if string.match(minimumyear or '', 'TCN') then minyear = -math.abs(minyear) end --allow BC qualifier (AD otherwise assumed)
	if string.match(maximumyear or '', 'TCN') then maxyear = -math.abs(maxyear) end --allow BC qualifier (AD otherwise assumed)
	
	if year == nil then
		errors = p.errorclass('Hàm nav_year không thể nhận ra năm được đưa vào tham số thứ 2 của nó.')
		return p.failedcat(errors, 'Y')
	end
	
	--AD/BC switches & vars
	
	local yearBCElastparts = { --needed for parent = AD 1-5, when the BC/E format is unknown
		--"BCE" removed to match both AD & BCE cats; easier & faster than multiple string.match()s
		['example_Hebrew people_example'] = 'BCE', --example entry format; add to & adjust as needed
	}
	local parentAD = nil  --following the "AD 1" convention from AD 1 to AD 10
	local parentBC = string.match(lastpart, '^TCN?') --following the "1 BC" convention for all years BC
	firstpart = mw.ustring.gsub(firstpart, '%s*SCN$', '') --handle AD/BC separately for easier & faster accounting
	lastpart  = mw.ustring.gsub(lastpart,  '^TCN?%s*', '')
	local BCe = parentBC or yearBCElastparts[lastpart] or 'TCN' --"TCN" default
	
	local year1to10 = (year >= 1 and year <= 10)
	local year1to10ADBC = year1to10 and (parentBC or parentAD) --special behavior 1-10 for low-# non-year series
	local year1to15AD = (year >= 1 and year <= 15 and not parentBC) --special behavior 1-15 for AD/BC display
	local switchADBC = 1                 --  1=AD parent
	if parentBC then switchADBC = -1 end -- -1=BC parent; possibly adjusted later
	local Y = 0 --secondary iterator for AD-on-a-BC-parent
	
	if minyear > year*switchADBC then minyear = year*switchADBC end --input error; minyear should be <= parent
	if maxyear < year*switchADBC then maxyear = year*switchADBC end --input error; maxyear should be >= parent
	
	local lspace = ' ' --leading space before year, after firstpart
	if string.match(firstpart, '[%-VW]$') then
		lspace = '' --e.g. "Straight-8 engines"
	end
	
	local tspace = ' ' --trailing space after year, before lastpart
	if string.match(lastpart, '^-') then
		tspace = '' --e.g. "2018-related timelines"
	end
	
	--determine interyear gap size to condense special category types, if possible
	local ygapdefault = 1 --assume/start at the most common case: 2001, 2002, etc.
	local ygap = ygapdefault
	if string.match(lastpart, 'presidential') then
		local ygap1, ygap2 = ygapdefault, ygapdefault --need to determine previous & next year gaps indepedently
		local ygap1_success, ygap2_success = false, false
		
		local prevseason = nil
		while ygap1 <= ygap_limit do --Czech Republic, Poland, Sri Lanka, etc. have 5-year terms
			prevseason = firstpart..lspace..(year-ygap1)..tspace..lastpart
			if catexists(prevseason) then
				ygap1_success = true
				break
			end
			ygap1 = ygap1 + 1
		end
		
		local nextseason = nil
		while ygap2 <= ygap_limit do --Czech Republic, Poland, Sri Lanka, etc. have 5-year terms
			nextseason = firstpart..lspace..(year+ygap2)..tspace..lastpart
			if catexists(nextseason) then
				ygap2_success = true
				break
			end
			ygap2 = ygap2 + 1
		end
		
		if ygap1_success and ygap2_success then
			if ygap1 == ygap2 then ygap = ygap1 end
		elseif ygap1_success then  ygap = ygap1
		elseif ygap2_success then  ygap = ygap2
		end
	end
	
	--skip non-existing years, if requested
	local ynogaps = {} --populate with existing years in the range, at most, [year - (skipgaps_limit * 5), year + (skipgaps_limit * 5)]
	if skipgaps then
		if minyear == minyear_default then
			minyear = 0 --automatically set minyear to 0, as AD/BC not supported anyway
		end
		if (year > 70) or --add support for AD/BC (<= AD 10) if/when needed
		   (minyear >= 0 and --must be a non-year series like "AC with 0 elements"
		   	not parentAD and not parentBC)
		then
			local yskipped = {} --track skipped y's to avoid double-checking
			local cat, found, Yeary
			
			 --populate nav element queue outwards positively from the parent
			local Year = year --to save/ratchet progression
			local i = 1
			while i <= 5 do
				local y = 1
				while y <= skipgaps_limit do
					found = false
					Yeary = Year + y
					if yskipped[Yeary] == nil then
						yskipped[Yeary] = Yeary
						cat = firstpart..lspace..Yeary..tspace..lastpart
						found = catexists(cat)
						if found then break end
					end
					y = y + 1
				end
				if found then Year = Yeary
				else          Year = Year + 1 end
				ynogaps[i] =  Year
				i = i + 1
			end
			
			ynogaps[0] = year --the parent
			
			--populate nav element queue outwards negatively from the parent
			Year = year --reset ratchet
			i = -1
			while i >= -5 do
				local y = -1
				while y >= -skipgaps_limit do
					found = false
					Yeary = Year + y
					if yskipped[Yeary] == nil then
						yskipped[Yeary] = Yeary
						cat = firstpart..lspace..Yeary..tspace..lastpart
						found = catexists(cat)
						if found then break end
					end
					y = y - 1
				end
				if found then Year = Yeary
				else          Year = Year - 1 end
				ynogaps[i] =  Year
				i = i - 1
			end
		else
			skipgaps = false --TODO: AD/BC support, then lift BC restrictions @ [[Template:Establishment category BC]] & [[Template:Year category header/core]]
		end
	end
	
	--begin navyears
	local navy = '<div class="toccolours categorySeriesNavigation-range">\n'
	
	local navlist = {}
	local y
	local j = 0 --decrementor for special cases "2021 World Rugby Sevens Series" -> "2021–2022"
	local i = -5 --nav position
	while i <= 5 do
		if skipgaps then
			y = ynogaps[i]
		else
			y = year + i*ygap*switchADBC - j
		end
		local BCdisp = ''
		if i ~= 0 then --left/right navy
			
			local AD = ''
			local BC = ''
			if year1to15AD and not
			   (year1to10 and not year1to10ADBC) --don't AD/BC 1-10's if parents don't contain AD/BC
			then
				if year >= 11 then --parent = AD 11-15
					if y <= 10 then --prepend AD on y = 1-10 cats only, per existing cats
						AD = ''
					end
					
				elseif year >= 1 then --parent = AD 1-10
					if y <= 0 then
						BC = BCe..' '
						y = math.abs(y - 1) --skip y = 0 (DNE)
					elseif y >= 1 and y <= 10 then --prepend AD on y = 1-10 cats only, per existing cats
						AD = ''
					end
				end
				
			elseif parentBC then
				if switchADBC == -1 then --displayed y is in the BC regime
					if y >= 1 then     --the common case
						BC = BCe..' '
					elseif y == 0 then --switch from BC to AD regime
						switchADBC = 1
					end
				end
				if switchADBC == 1 then --displayed y is now in the AD regime
					Y = Y + 1 --skip y = 0 (DNE)
					y = Y     --easiest solution: start another iterator for these AD y's displayed on a BC year parent
					AD = ''
				end
			end
			if BC ~= '' and year <= 5 then --only show 'TCN' for parent years <= 5: saves room, easier to read,
				BCdisp = ' '..BCe          --and 6 is the first/last nav year that doesn't need a disambiguator;
			end                            --the center/parent year will always show BC, so no need to show it another 10x
			
			--populate left/right navy
			local ysign = y --use y for display & ysign for logic
			local disp = y..BCdisp
			if BC ~= '' then ysign = -ysign end
			local firsttry = firstpart..lspace..AD..y..tspace..BC..lastpart
			if (minyear <= ysign) and (ysign <= maxyear) then
				local catlinkAD = catlinkfollowr( frame, firsttry, disp ) --try AD
				local catlink = catlinkAD --tentative winner
				if AD ~= '' then --for "ACArt with 5 suppressed elements"-type cats
					local catlinkNoAD = catlinkfollowr( frame, firstpart..lspace..y..tspace..BC..lastpart, disp ) --try !AD
					if catlinkNoAD.catexists == true then
						catlink = catlinkNoAD --usurp
					elseif listall then
						tlistall[#tlistall] = tlistall[#tlistall]..' (tried; not displayed)<sup>1</sup>'
					end
				end
				if (AD..BC == '') and (catlink.catexists == false) and (y >= 1000) then --!ADBC & DNE; 4-digit only, to be frugal
					--try basic hyphenated cats: 1-year, endash, CNBS-correct only, no #Rs
					local yHyph_4 = y..'–'..(y+1) --try 2010–2011 type cats
					local catlinkHyph_4 = catlinkfollowr( frame, firstpart..lspace..yHyph_4..tspace..BC..lastpart, yHyph_4 )
					if catlinkHyph_4.catexists and catlinkHyph_4.rtarget == nil then --exists & no #Rs
						catlink = catlinkHyph_4 --usurp
						trackcat(27, 'Category series navigation năm và khoảng')
					else
						if listall then
							tlistall[#tlistall] = tlistall[#tlistall]..' (tried; not displayed)<sup>2</sup>'
						end
						local yHyph_2 = y..'–'..string.match(y+1, '%d%d$') --try 2010–11 type cats
						if i == 1 then
							local yHyph_2_special = (y-1)..'–'..string.match(y, '%d%d$') --try special case 2021 -> 2021–22
							local catlinkHyph_2_special = catlinkfollowr( frame, firstpart..lspace..yHyph_2_special..tspace..BC..lastpart, yHyph_2_special )
							if catlinkHyph_2_special.catexists and catlinkHyph_2_special.rtarget == nil then --exists & no #Rs
								catlink = catlinkHyph_2_special --usurp
								trackcat(27, 'Category series navigation năm và khoảng')
								j = 1
							elseif listall then
								tlistall[#tlistall] = tlistall[#tlistall]..' (tried; not displayed)<sup>3</sup>'
							end
						end
						if not (i == 1 and j == 1) then
							local catlinkHyph_2 = catlinkfollowr( frame, firstpart..lspace..yHyph_2..tspace..BC..lastpart, yHyph_2 )
							if catlinkHyph_2.catexists and catlinkHyph_2.rtarget == nil then --exists & no #Rs
								catlink = catlinkHyph_2 --usurp
								trackcat(27, 'Category series navigation năm và khoảng')
							elseif listall then
								tlistall[#tlistall] = tlistall[#tlistall]..' (tried; not displayed)<sup>4</sup>'
							end
						end
					end
				end
				if catlink.rtarget then --#R followed; determine why
					local r = catlink.rtarget
					local c = catlink.cat
					local year_regex  = '%d%d%d%d[–-]?%d?%d?%d?%d?' --prioritize year/range stripping, e.g. for "2006 Super 14 season"
					local hyph_regex  = '%d%d%d%d[–-]%d+' --stricter
					local num_regex   = '%d+' --strip any number otherwise
					local final_regex = nil   --best choice goes here
					if mw.ustring.match(r, year_regex) and mw.ustring.match(c, year_regex) then
						final_regex = year_regex
					elseif mw.ustring.match(r, num_regex) and mw.ustring.match(c, num_regex) then
						final_regex = num_regex
					end
					if final_regex then
						local r_base = mw.ustring.gsub(r, final_regex, '')
						local c_base = mw.ustring.gsub(c, final_regex, '')
						if r_base ~= c_base then
							trackcat(19, 'Category series navigation có năm đã đổi hướng (thay đổi gốc)') --acceptable #R target
						elseif mw.ustring.match(r, hyph_regex) then
							trackcat(20, 'Category series navigation có năm đã đổi hướng (thay đổi var)') --e.g. "2008 in Scottish women's football" to "2008–09"
						else
							trackcat(21, 'Category series navigation có năm đã đổi hướng (khác)') --exceptions go here
						end
					else
						trackcat(20, 'Category series navigation có năm đã đổi hướng (thay đổi var)') --e.g. "V2 engines" to "V-twin engines"
					end
				end
				table.insert(navlist, catlink.navelement)
			else --OOB vs min/max
				local hidden = '<span style="visibility:hidden">'..disp..'</span>'
				table.insert(navlist, hidden)
				if listall then
					local dummy = catlinkfollowr( frame, firsttry, disp )
					tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
				end
			end
		else --center navy
			if parentBC then BCdisp = ' '..BCe end
			table.insert(navlist, '<b>'..year..BCdisp..'</b>')
		end
		
		i = i + 1
	end
	
	--add the list
	navy = navy..horizontal(navlist)..'\n'
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navy..'</div>'
	end
end


--[[==========================={{  nav_roman  }}==============================]]

local function nav_roman( frame, firstpart, roman, lastpart, minimumrom, maximumrom )
	local toarabic = require('Module:ConvertNumeric').roman_to_numeral
	local toroman  = require('Module:Roman').main
	
	--sterilize/convert rom/num
	local num = tonumber(toarabic(roman))
	local rom = toroman({ [1] = num })
	if num == nil or rom == nil then --out of range or some other error
		errors = p.errorclass('Hàm nav_roman không thể nhận ra một hoặc nhiều "'..(num or 'nil')..'" & "'..
							(rom or 'nil')..'" trong thể loại "'..firstpart..' '..roman..' '..lastpart..'".')
		return p.failedcat(errors, 'R')
	end
	
	--sterilize min/max
	local minrom = tonumber(minimumrom or '') or tonumber(toarabic(minimumrom or ''))
	local maxrom = tonumber(maximumrom or '') or tonumber(toarabic(maximumrom or ''))
	if minrom < 1 then minrom = 1 end    --toarabic() returns -1 on error
	if maxrom < 1 then maxrom = 9999 end --toarabic() returns -1 on error
	if minrom > num then minrom = num end
	if maxrom < num then maxrom = num end
	
	--begin navroman
	local navr = '<div class="toccolours categorySeriesNavigation-range">\n'
	
	local navlist = {}
	local i = -5 --nav position
	while i <= 5 do
		local n = num + i
		
		if n >= 1 then
			local r = toroman({ [1] = n })
			if i ~= 0 then --left/right navr
				local catlink = catlinkfollowr( frame, firstpart..' '..r..' '..lastpart, r )
				if minrom <= n and n <= maxrom then
					if catlink.rtarget then --a {{Đổi hướng thể loại}} was followed
						trackcat(22, 'Category series navigation có số La Mã đã đổi hướng')
					end
					table.insert(navlist, catlink.navelement)
				else
					local hidden = '<span style="visibility:hidden">'..r..'</span>'
					table.insert(navlist, hidden)
					if listall then
						tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
					end
				end
			else --center navr
				table.insert(navlist, '<b>'..r..'</b>')
			end
		else
			table.insert(navlist, '<span style="visibility:hidden">I</span>')
		end
		
		i = i + 1
	end
	
	-- add the list
	navr = navr..horizontal(navlist)..'\n'
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navr..'</div>'
	end
end


--[[=========================={{  nav_nordinal  }}============================]]

local function nav_nordinal( frame, firstpart, ord, lastpart, minimumord, maximumord )
	local nord = tonumber(ord)
	local minord = tonumber(string.match(minimumord or '', '(-?%d+)')) or -9999 --allow full ord & +/- qualifier
	local maxord = tonumber(string.match(maximumord or '', '(-?%d+)')) or  9999 --allow full ord & +/- qualifier
	if string.match(minimumord or '', 'TCN') then minord = -math.abs(minord) end --allow BC qualifier (AD otherwise assumed)
	if string.match(maximumord or '', 'TCN') then maxord = -math.abs(maxord) end --allow BC qualifier (AD otherwise assumed)
	
	local temporal = string.match(lastpart, 'thế kỷ') or
					 string.match(lastpart, 'thiên niên kỷ')
	
	local tspace = ' ' --assume a trailing space after ordinal
	if string.match(lastpart, '^-') then tspace = '' end --DNE for "19th-century"-type cats
	
	--AD/BC switches & vars
	
	local ordBCElastparts = { --needed for parent = AD 1-5, when the BC/E format is unknown
		--lists the lastpart of valid BCE cats
		--"BCE" removed to match both AD & BCE cats; easier & faster than multiple string.match()s
		['-century Hebrew people'] = 'TCN', --WP:CFD/Log/2016 June 21#Category:11th-century BC Hebrew people
		['-century Jews']          = 'TCN', --co-nominated
		['-century Judaism']       = 'TCN', --co-nominated
		['-century rabbis']        = 'TCN', --co-nominated
		['-century High Priests of Israel'] = 'TCN',
	}
	local parentBC = mw.ustring.match(lastpart, '%s(TCN?)')       --"1st-century BC" format
	local lastpartNoBC = mw.ustring.gsub(lastpart, '%sTCN?', '')  --easier than splitting lastpart up in 2; AD never used
	local BCe = parentBC or ordBCElastparts[lastpartNoBC] or 'TCN' --"BC" default
	
	local switchADBC = 1                 --  1=AD parent
	if parentBC then switchADBC = -1 end -- -1=BC parent; possibly adjusted later
	local O = 0 --secondary iterator for AD-on-a-BC-parent
	
	if not temporal and minord < 1 then minord = 1 end --nothing before "1st parliament", etc.
	if minord > nord*switchADBC then minord = nord*switchADBC end --input error; minord should be <= parent
	if maxord < nord*switchADBC then maxord = nord*switchADBC end --input error; maxord should be >= parent
	
	--begin navnordinal
	local bnb = '' --border/no border
	if navborder == false then --for Category series navigation decade and century
		bnb = 'categorySeriesNavigation-range-transparent'
	end
	local navo = '<div class="toccolours categorySeriesNavigation-range '..bnb..'">\n'
	
	local navlist = {}
	local i = -5 --nav position
	while i <= 5 do
		local o = nord + i*switchADBC
		local BC = ''
		local BCdisp = ''
		if parentBC then
			if switchADBC == -1 then --parentBC looking at the BC side
				if o >= 1 then     --the common case
					BC = ' '..BCe
				elseif o == 0 then --switch to the AD side
					BC = ''
					switchADBC = 1
				end
			end
			if switchADBC == 1 then --displayed o is now in the AD regime
				O = O + 1 --skip o = 0 (DNE)
				o = O     --easiest solution: start another iterator for these AD o's displayed on a BC year parent
			end
		elseif o <= 0 then --parentAD looking at BC side
			BC = ' '..BCe
			o = math.abs(o - 1) --skip o = 0 (DNE)
		end
		if BC ~= '' and nord <= 5 then --only show 'TCN' for parent ords <= 5: saves room, easier to read,
			BCdisp = ' '..BCe          --and 6 is the first/last nav ord that doesn't need a disambiguator;
		end                            --the center/parent ord will always show BC, so no need to show it another 10x
		
		--populate left/right navo
		local oth = p.addord(o)
		local osign = o --use o for display & osign for logic
		if BC ~= '' then osign = -osign end
		local hidden = '<span style="visibility:hidden">'..oth..'</span>'
		if temporal then --e.g. "3rd-century BC"
			local lastpart = lastpartNoBC --lest we recursively add multiple "BC"s
			if BC ~= '' then
				lastpart = string.gsub(lastpart, temporal, temporal..BC) --replace BC if needed
			end
			local catlink = catlinkfollowr( frame, firstpart..' '..oth..tspace..lastpart, oth..BCdisp )
			if (minord <= osign) and (osign <= maxord) then
				if catlink.rtarget then --a {{Đổi hướng thể loại}} was followed
					trackcat(23, 'Category series navigation có số thứ tự đã đổi hướng')
				end
				table.insert(navlist, navcenter(i, catlink))
			else
				table.insert(navlist, hidden)
				if listall then
					tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
				end
			end
		elseif BC == '' and minord <= osign and osign <= maxord then --e.g. >= "1st parliament"
			local catlink = catlinkfollowr( frame, firstpart..' '..oth..tspace..lastpart, oth )
			if catlink.rtarget then --a {{Đổi hướng thể loại}} was followed
				trackcat(23, 'Category series navigation có số thứ tự đã đổi hướng')
			end
			table.insert(navlist, navcenter(i, catlink))
		else --either out-of-range (hide), or non-temporal + BC = something might be wrong (2nd X parliament BC?); handle exceptions if/as they arise
			table.insert(navlist, hidden)
		end
		
		i = i + 1
	end
	
	navo = navo..horizontal(navlist)..'\n'
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navo..'</div>'
	end
end


--[[========================={{  nav_wordinal  }}=============================]]

local function nav_wordinal( frame, firstpart, word, lastpart, minimumword, maximumword, ordinal, frame )
	--Module:ConvertNumeric.spell_number2() args:
	--   ordinal == true : 'second' is output instead of 'two'
	--   ordinal == false: 'two' is output instead of 'second'
	local ord2viet = require('Module:ConvertNumeric').spell_number2
	local viet2ord = require('Module:ConvertNumeric').vietnamese_to_numeral
	local th = 'th'
	if not ordinal then
		th = ''
		viet2ord = require('Module:ConvertNumeric').vietnamese_to_numeral
	end
	local capitalize = nil ~= string.match(word, '^%u') --determine capitalization
	local nord = viet2ord(string.lower(word)) --operate on/with lowercase, and restore any capitalization later
	
	local lspace = ' ' --assume a leading space (most common)
	local tspace = ' ' --assume a trailing space (most common)
	if string.match(firstpart, '[%-%(]$') then lspace = '' end --DNE for "Straight-eight engines"-type cats
	if string.match(lastpart, '^[%-%)]' ) then tspace = '' end --DNE for "Nine-cylinder engines"-type cats
	
	--sterilize min/max
	local maxword_default = 99
	local maxword = maxword_default
	local minword = 1
	if minimumword then
		local num = tonumber(minimumword)
		if num and 0 < num and num < maxword then
			minword = num
		else
			local ord = viet2ord(minimumword)
			if 0 < ord and ord < maxword then
				minword = ord
			end
		end
	end
	if maximumword then
		local num = tonumber(maximumword)
		if num and 0 < num and num < maxword then
			maxword = num
		else
			local ord = viet2ord(maximumword)
			if 0 < ord and ord < maxword then
				maxword = ord
			end
		end
	end
	if minword > nord then minword = nord end
	if maxword < nord then maxword = nord end
	
	--determine max existing cat
	local listoverride = true
	local n_max = nord
	local m = 1
	while m <= 5 do
		local n = nord + m
		local nth = p.addord(n)
		if not ordinal then nth = n end
		local w = ord2viet{ num = n, ordinal = ordinal, capitalize = capitalize }
		local catlink = catlinkfollowr( frame, firstpart..lspace..w..tspace..lastpart, nth, nil, listoverride )
		if catlink.catexists then n_max = n end
		m = m + 1
	end
	
	--begin navwordinal
	local navw = '<div class="toccolours categorySeriesNavigation-range">\n'
	
	local navlist = {}
	local prepad = ''
	local i = -5 --nav position
	while i <= 5 do
		local n = nord + i
		
		if n >= 1 then
			local nth = p.addord(n)
			if not ordinal then nth = n end
			if i ~= 0 then --left/right navw
				local w = ord2viet{ num = n, ordinal = ordinal, capitalize = capitalize }
				local catlink = catlinkfollowr( frame, firstpart..lspace..w..tspace..lastpart, nth )
				if minword <= n and n <= maxword then
					if catlink.rtarget then --a {{Đổi hướng thể loại}} was followed
						trackcat(24, 'Category series navigation có từ thứ tự đã đổi hướng')
					end
					if n <= n_max or
					   maxword ~= maxword_default
					then
						table.insert(navlist, prepad..catlink.navelement) --display normally
						prepad = ''
					else
						local postpad = '<span style="visibility:hidden"> • '..nth..'</span>'
						navlist[#navlist] = (navlist[#navlist] or '')..postpad
						if listall then tlistall[#tlistall] = tlistall[#tlistall]..' ('..postpad..')' end
					end
				else
					local postpad = '<span style="visibility:hidden"> • '..nth..'</span>'
					navlist[#navlist] = (navlist[#navlist] or '')..postpad
					if listall then tlistall[#tlistall] = tlistall[#tlistall]..' ('..postpad..')' end
				end
			else --center navw
				table.insert(navlist, prepad..'<b>'..nth..'</b>')
				prepad = ''
			end
		else --n < 1
			prepad = prepad..'<span style="visibility:hidden"> • '..'0'..th..'</span>'
			if listall then tlistall[#tlistall] = (tlistall[#tlistall] or '')..' (x)' end
		end
		
		i = i + 1
	end
	-- Add the list
	navw = navw..horizontal(navlist)..'\n'
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navw..'</div>'
	end
end


--[[==========================={{  find_var  }}===============================]]

local function find_var( pn )
	--Extracts the variable text (e.g. 2015, 2015–16, 2000s, 3rd, III, etc.) from a string,
	--and returns { ['vtype'] = <'year'|'season'|etc.>, <v> = <2015|2015–16|etc.> }
	local pagename = currtitle.text
	if pn and pn ~= '' then
		pagename = pn
	end
	
	local cpagename = 'Thể loại:'..pagename --limited-Lua-regex workaround
	
	local d_season = mw.ustring.match(cpagename, ':(%d+s).+%(%d+[–-]%d+%)') --i.e. "1760s in the Province of Quebec (1763–1791)"
	
	local y_season = mw.ustring.match(cpagename, ':(%d+) .+%(%d+[–-]%d+%)') --i.e. "1763 establishments in the Province of Quebec (1763–1791)"
	
	local e_season = mw.ustring.match(cpagename, '%s(%d+[–-])$') or --irreg; ending unknown, e.g. "Members of the Scottish Parliament 2021–"
					 mw.ustring.match(cpagename, '%s(%d+[–-]nay)$') --e.g. "UK MPs 2019–present"
	
	local season   = mw.ustring.match(cpagename, '[:%s%(](%d+[–-]%d+)[%)%s]') or --split in 2 b/c you can't frontier '$'/eos?
					 mw.ustring.match(cpagename, '[:%s](%d+[–-]%d+)$')
	
	local tvseason = mw.ustring.match(cpagename, 'mùa (%d+)') or
					 mw.ustring.match(cpagename, 'series (%d+)')
	
	local nordinal = mw.ustring.match(cpagename, '[:%s](%d+)[-%s]') or
					 mw.ustring.match(cpagename, '[:%s](%d+)$')
	
	local decade   = mw.ustring.match(cpagename, '[:%s][Tt]hập niên (%d+)[%s-]') or
					 mw.ustring.match(cpagename, '[:%s][Tt]hập niên (%d+)$')
	
	local year     = mw.ustring.match(cpagename, '[:%s][Nn]ăm (%d%d%d%d)%s') or --prioritize 4-digit years
					 mw.ustring.match(cpagename, '[:%s][Nn]ăm (%d%d%d%d)$') or
					 mw.ustring.match(cpagename, '[:%s][Nn]ăm (%d+)%s') or
					 mw.ustring.match(cpagename, '[:%s][Nn]ăm (%d+)$') or
					 --expand/combine exceptions below as needed
					--  mw.ustring.match(cpagename, '[:%s](%d+)-related') or
					--  mw.ustring.match(cpagename, '[:%s](%d+)-cylinder') or
					 mw.ustring.match(cpagename, '[:%-VW](%d+)%s') --e.g. "Straight-8 engines"
	
	local roman    = mw.ustring.match(cpagename, '%s([IVXLCDM]+)%s')
	
	local found    = d_season or y_season or e_season or season or tvseason or
					 nordinal or decade or year or roman
	
	if found then
		if string.match(found, '%d%d%d%d%d') == nil then
			--return in order of decreasing complexity/chance for duplication
			if nordinal and season --i.e. "18th-century establishments in the Province of Quebec (1763–1791)"
						then return { ['vtype'] = 'nordinal', ['v'] = nordinal } end
			if d_season then return { ['vtype'] = 'decade',   ['v'] = d_season } end
			if y_season then return { ['vtype'] = 'year',     ['v'] = y_season } end
			if e_season then return { ['vtype'] = 'ending',   ['v'] = e_season } end
			if season   then return { ['vtype'] = 'season',   ['v'] = season   } end
			if tvseason then return { ['vtype'] = 'tvseason', ['v'] = tvseason } end
			-- giữ nguyên thứ tự decade, year, nordinal
			if decade   then return { ['vtype'] = 'decade',   ['v'] = decade   } end
			if year     then return { ['vtype'] = 'year',     ['v'] = year     } end
			if nordinal then return { ['vtype'] = 'nordinal', ['v'] = nordinal } end
			if roman    then return { ['vtype'] = 'roman',    ['v'] = roman    } end
		end
	else
		--try wordinals ('zeroth' to 'ninety-ninth' only)
		local viet2ord = require('Module:ConvertNumeric').vietnamese_to_numeral
		local split = mw.text.split(pagename, ' ')
		for i=1, #split do
			if viet2ord(split[i]) > -1 then
				return { ['vtype'] = 'wordinal', ['v'] = split[i] }
			end
		end
		
		--try Vietnamese numerics ('one'/'single' to 'ninety-nine' only)
		local viet2num = require('Module:ConvertNumeric').vietnamese_to_numeral
		local split = mw.text.split(pagename, '[%s%-]') --e.g. "Nine-cylinder engines"
		for i=1, #split do
			if viet2num(split[i]) > -1 then
				return { ['vtype'] = 'enumeric', ['v'] = split[i] }
			end
		end
	end
	
	errors = p.errorclass('Hàm find_var không thể tìm văn bản biến trong thể loại "'..pagename..'".')
	return { ['vtype'] = 'error', ['v'] = p.failedcat(errors, 'V') }
end


--[[==========================================================================]]
--[[                                  Main                                    ]]
--[[==========================================================================]]

function p.csn( frame )
	--arg checks & handling
	local args = frame:getParent().args
	checkforunknownparams(args)       --for template args
	checkforunknownparams(frame.args) --for #invoke'd args
	local cat  = args['cat']                --'testcase' alias for catspace
	local list = args['list-all-links']     --debugging utility to output all links & followed #Rs
	local follow = args['follow-redirects'] --default 'yes'
	local testcase    = args['testcase']
	local testcasegap = args['testcasegap']
	local minimum = args['min']
	local maximum = args['max']
	local skip_gaps = args['skip-gaps']
	local show = args['show']
	
	if show and show ~= '' then
		if show == 'skip-gaps'  then return skipgaps_limit
		elseif show == 'term-limit' then return term_limit
		elseif show == 'hgap-limit' then return hgap_limit
		elseif show == 'ygap-limit' then return ygap_limit end
	end
	
	--apply args
	local pagename = testcase or cat or currtitle.text
	local testcaseindent = ''
	if testcasecolon == ':' then testcaseindent = '\n::' end
	if follow and follow == 'no' then followRs = false end
	if list and list == 'yes' then listall = true end
	if skip_gaps and skip_gaps == 'yes' then
		skipgaps = true
		trackcat(26, 'Category series navigation sử dụng tham số skip-gaps')
	end
	
	--ns checks
	if currtitle.nsText == 'Thể_loại' then
		if cat and cat ~= '' then
			trackcat(1, 'Category series navigation sử dụng tham số cat')
		end
		if testcase and testcase ~= '' then
			trackcat(2, 'Category series navigation sử dụng tham số testcase')
		end
	elseif currtitle.nsText == '' then
		trackcat(30, 'Category series navigation trong không gian tên chính')
	end
	
	--find the variable parts of pagename
	local findvar = find_var(pagename)
	if findvar.vtype == 'error' then --basic format error checking in find_var()
		return findvar.v..table.concat(ttrackingcats)
	end
	local start = string.match(findvar.v, '^%d+')
	
	--the rest is static
	local findvar_escaped = string.gsub( findvar.v, '%-', '%%%-')
	local firstpart, lastpart = string.match(pagename, '^(.-)'..findvar_escaped..'(.*)$')
	if findvar.vtype == 'tvseason' then --double check for cases like "30 Rock (season 3) episodes"
		firstpart, lastpart = string.match(pagename, '^(.-season )'..findvar_escaped..'(.*)$')
		if firstpart == nil then
			firstpart, lastpart = string.match(pagename, '^(.-series )'..findvar_escaped..'(.*)$')
		end
	end
	firstpart = mw.text.trim(firstpart or '')
	lastpart  = mw.text.trim(lastpart or '')

	--call the appropriate nav function, in order of decreasing popularity
	if findvar.vtype == 'year' then     --e.g. "500", "2001"; nav_year..nav_decade; ~75% of cats
		local nav1 = nav_year( frame, firstpart, start, lastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats)
		
		local dec = math.floor(findvar.v/10)
		local decadecat = nil
		local firstpart_dec = firstpart:gsub('[Nn]ăm', 'thập niên')
		if firstpart_dec == 'SCN' and dec <= 1 then
			firstpart_dec = ''
			if dec == 0 then dec = '' end
		end
		local decade = dec..'0 '
		decadecat = mw.text.trim( firstpart_dec..' '..decade..lastpart )
		local exists = catexists(decadecat)
		if exists then
			navborder = false
			trackcat(28, 'Category series navigation năm và thập niên')
			local nav2 = nav_decade( frame, firstpart_dec, decade, lastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats)
			return wrap( nav1, nav2 )
		elseif ttrackingcats[16] ~= '' then --nav_year isolated; check nav_hyphen (e.g. UK MPs 1974, Moldovan MPs 2009, etc.)
			local hyphen = '–'
			local finish = start
			local nav2 = nav_hyphen( frame, start, hyphen, finish, firstpart, lastpart, minimum, maximum, testcasegap )..testcaseindent..table.concat(ttrackingcats)
			if ttrackingcats[16] ~= '' then return wrap( nav1 ) --still isolated; rv to nav_year
			else return wrap( nav2 ) end
		else --regular nav_year
			return wrap( nav1 )
		end
		
	elseif findvar.vtype == 'decade' then   --e.g. "0s", "2010s"; nav_decade..nav_nordinal; ~12% of cats
		local nav1 = nav_decade( frame, firstpart, start, lastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats)
		
		local decade = tonumber(string.match(findvar.v, '^(%d+)'))
		local century = math.floor( ((decade-1)/100) + 1 ) --from {{CENTURY}}
		if century == 0 then century = 1 end --no 0th century
		if string.match(decade, '00$') then
			century = century + 1 --'2000' is in the 20th, but the rest of the 2000s is in the 21st
		end
		firstpart = firstpart:gsub('([Tt])hập niên', '%1hế kỷ')
		local clastpart = lastpart
		local centurycat = mw.text.trim( firstpart..' '..p.addord(century)..' '..clastpart )
		local exists = catexists(centurycat)
		if exists then
			navborder = false
			trackcat(29, 'Category series navigation thập niên và thế kỷ')
			local nav2 = nav_nordinal( frame, firstpart, century, clastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats)
			return wrap( nav1, nav2 )
		else
			return wrap( nav1 )
		end
		
	elseif findvar.vtype == 'nordinal' then --e.g. "1st", "99th"; ~7.5% of cats
		return wrap( nav_nordinal( frame, firstpart, start, lastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats) )
		
	elseif findvar.vtype == 'season' then   --e.g. "1–4", "1999–2000", "2001–02", "2001–2002", "2005–2010", etc.; ~5.25%
		local hyphen, finish = mw.ustring.match(findvar.v, '%d([–-])(%d+)') --ascii 150 & 45 (ndash & keyboard hyphen); mw req'd
		return wrap( nav_hyphen( frame, start, hyphen, finish, firstpart, lastpart, minimum, maximum, testcasegap )..testcaseindent..table.concat(ttrackingcats) )
		
	elseif findvar.vtype == 'tvseason' then --e.g. "1", "15" but preceded with "season" or "series"; <1% of cats
		return wrap( nav_tvseason( frame, firstpart, start, lastpart, maximum )..testcaseindent..table.concat(ttrackingcats) ) --"minimum" defaults to 1
		
	elseif findvar.vtype == 'wordinal' then --e.g. "first", "ninety-ninth"; <<1% of cats
		local ordinal = true
		return wrap( nav_wordinal( frame, firstpart, findvar.v, lastpart, minimum, maximum, ordinal, frame )..testcaseindent..table.concat(ttrackingcats) )
		
	elseif findvar.vtype == 'enumeric' then --e.g. "one", "ninety-nine"; <<1% of cats
		local ordinal = false
		return wrap( nav_wordinal( frame, firstpart, findvar.v, lastpart, minimum, maximum, ordinal, frame )..testcaseindent..table.concat(ttrackingcats) )
		
	elseif findvar.vtype == 'roman' then    --e.g. "I", "XXVIII"; <<1% of cats
		return wrap( nav_roman( frame, firstpart, findvar.v, lastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats) )
		
	elseif findvar.vtype == 'ending' then   --e.g. "2021–" (irregular; ending unknown); <<<1% of cats
		local hyphen, finish = mw.ustring.match(findvar.v, '%d([–-])nay$'), -1 --ascii 150 & 45 (ndash & keyboard hyphen); mw req'd
		if hyphen == nil then
			hyphen, finish = mw.ustring.match(findvar.v, '%d([–-])$'), 0 --0/-1 are hardcoded switches for nav_hyphen()
		end
		return wrap( nav_hyphen( frame, start, hyphen, finish, firstpart, lastpart, minimum, maximum, testcasegap )..testcaseindent..table.concat(ttrackingcats) )
		
	else                                 --malformed
		errors = p.errorclass('Không thể xác định hàm nav phù hợp từ khoảng thời gian không đúng định dạng "'..findvar.v..'". ')
		return p.failedcat(errors, 'N')..table.concat(ttrackingcats)
	end
end

return p