Module:Navseasoncats

This Lua module is used on approximately 448,000 pages, or roughly 1113% of all pages.
To avoid major disruption and server load, any changes should be tested in the module's /sandbox or /testcases subpages, or in your own module sandbox. The tested changes can be added to this page in a single edit. Consider discussing changes on the talk page before implementing them.

This module depends on the following other modules:

About

{{Navseasoncats}} is intended to be a minimal-input, near-universal template for navigating most sequential categories.

Type Example category BC(E)? Example output

Season 2001–02 FA Cup No Lua error in mw.title.lua at line 209: too many expensive function calls.

TV season Futurama (season 1) episodes – Lua error in mw.title.lua at line 209: too many expensive function calls.

Office term (regular) MEPs 2004–2009 No Lua error in mw.title.lua at line 209: too many expensive function calls.

Office term (irregular) Wales AMs 2003–2007 No Lua error in mw.title.lua at line 209: too many expensive function calls.

Numerical range

Taxonbars with 30–34 taxon IDs

–

15–19
20–24
25–29
30–34
35–39
40–44
45–49

Decade 1990s in Scotland BC Lua error in mw.title.lua at line 209: too many expensive function calls.

Year 1999 in Scotland BC(E) Lua error in mw.title.lua at line 209: too many expensive function calls.

Year (auto-condensed) Candidates in the 2000 US presidential election – Lua error in mw.title.lua at line 209: too many expensive function calls.

Year (|skip-gaps=yes) Amusement parks opened in 1880 – Lua error in mw.title.lua at line 209: too many expensive function calls.

Ordinal (temporal) 2nd-century rabbis BC(E) Lua error in mw.title.lua at line 209: too many expensive function calls.

Ordinal (numeric) 1st Lok Sabha members – Lua error in mw.title.lua at line 209: too many expensive function calls.

Ordinal (word) First Dynasty of Egypt – Lua error in mw.title.lua at line 209: too many expensive function calls.

Roman numeral Deputies of Legislature X of the Kingdom of Italy – Lua error in mw.title.lua at line 209: too many expensive function calls.

Mixed decade 1760s in the Province of Quebec (1763–1791) – Lua error in mw.title.lua at line 209: too many expensive function calls.

Mixed year 1778 establishments in the Province of Quebec (1763–1791) – Lua error in mw.title.lua at line 209: too many expensive function calls.

Searching behavior

Most multi-year seasons/office terms/numerical ranges are acceptable, as long as the season duration/term length/range size is <= 10, and the gap between seasons is <= 6. For series exceeding either of these criteria, see/use {{Irregular navseasoncats}}.

The length of each season is automatically determined from the originating category name, up to and including 10 years. MOS:DATERANGE compliance is preferred, but some deviation is allowed and tracked for regular series with seasons > 1 year long. {{Category redirect}}s are followed, and tracked for either MOS contravention (to be corrected) or for navigational aid (no error). The gap size between successive seasons is also automatically determined, up to and including 5 years, and defaults to 0 (e.g. 1995–96 → 1996–97).

Automatically condensed years are supported for presidential categories only (but can be easily expanded as needed), for gaps up to and including 5 years, and defaults to 1. To skip gaps of up to 25 years in any year categories, use |skip-gaps=yes.

Limitations

Numerical limitations & AD/BC/E

Season/office term categories do not work for any years BC, which will be hidden, because no working examples were found.
Decade categories recognize BC, but not BCE, because no working examples were found.
Ordinal & numeral words do not work above the ninety-ninth & ninety-nine, because no working examples were found.

Condensation

Automatically condensed Olympics display is not supported due to peculiarities; use {{Winter Olympics by year category navigation}}, etc., instead.
Automatically condensed years are supported for presidential categories only, due to their consistency; use |skip-gaps=yes as desired elsewhere.

Work-arounds

Base-name changes: create at least 2 logically numbered {{R from category navigation}} (1 forward & 1 backward), to join both related series.
Unaccounted-for name+number conventions: where a fixed number is part of the prefix text, e.g. Chapter 11 bankruptcies, a non-breaking space may force the template to work. See this fix, where {{title year}} skipped over 11 as part of a word rather than a discrete number. (This has been accounted for and is no longer required in this example.)
General: for large, permanent gaps^† between successive categories, use {{Succeeding category}}, {{Preceding category}}, {{Category pair}}, as needed, in addition to {{Navseasoncats}} on both sides, or in the middle, of the gap. Even if {{Navseasoncats}} is isolated, it has the benefit of confirming the absence of nearby categories to the reader or maintainer.
^†Permanent gaps, where there is confirmed to be an absence of data, and not just a current, yet to be filled, gap on Wikipedia.

Related CfDs

Usage

Typical usage

{{Navseasoncats}}

Specify a minimum and/or maximum year to display

{{Navseasoncats|min=-100}}
{{Navseasoncats|min=100 BC}}
{{Navseasoncats|min=1753|max=1810}}
{{Navseasoncats|max=2025}}

To skip gaps in year categories

{{Navseasoncats|skip-gaps=yes}}

To not automatically follow {{Category redirect}}s

{{Navseasoncats|follow-redirects=no}}

Exceptional cases

{{Navseasoncats|cat=2010s albums}} — to behave as if placed on |cat=; consider using {{Category pair}} instead of |cat=

Testing & debugging

To test the output of the template on a particular category name, use the |testcase= parameter, and |testcasegap= if necessary:

{{Navseasoncats |testcase=1770s in the Province of Quebec (1763–1791) |min=1760}} →

Lua error in mw.title.lua at line 209: too many expensive function calls.

{{Navseasoncats |testcase=1770s in the Province of Quebec (1763–1791) |max=1970s}} →

Lua error in mw.title.lua at line 209: too many expensive function calls.
To see all links produced and/or tested, and what effect each has on their display, use |list-all-links=yes:

{{Navseasoncats |testcase=Nations at the 2013 World Athletics Championships |min=2008 |skip-gaps=yes |list-all-links=yes}} →

Category:Nations at the 2006 World Athletics Championships (2006) (2006)
Category:Nations at the 2007 World Athletics Championships (2007) (2007)
Category:Nations at the 2008 World Athletics Championships (2008)
Category:Nations at the 2008–2009 World Athletics Championships (2008–2009) (tried; not displayed)
Category:Nations at the 2008–09 World Athletics Championships (2008–09) (tried; not displayed)
Category:Nations at the 2009 World Athletics Championships → Category:Nations at the 2009 World Championships in Athletics (2009)
Category:Nations at the 2011 World Athletics Championships → Category:Nations at the 2011 World Championships in Athletics (2011)
Category:Nations at the 2015 World Athletics Championships → Category:Nations at the 2015 World Championships in Athletics (2015)
Category:Nations at the 2017 World Athletics Championships → Category:Nations at the 2017 World Championships in Athletics (2017)
Category:Nations at the 2019 World Athletics Championships (2019)
Category:Nations at the 2020 World Athletics Championships (2020)
Category:Nations at the 2020–2021 World Athletics Championships (2020–2021) (tried; not displayed)
Category:Nations at the 2020–21 World Athletics Championships (2020–21) (tried; not displayed)
Category:Nations at the 2021 World Athletics Championships (2021)
Category:Nations at the 2021–2022 World Athletics Championships (2021–2022) (tried; not displayed)
Category:Nations at the 2021–22 World Athletics Championships (2021–22) (tried; not displayed)

All possible element types are shown above (blue, red/grey, hidden, and redirect), and would otherwise display as:

2006
2007
2008
2009
2011
2013
2015
2017
2019
2020
2021

Tracking categories

Purge this page to update the totals

If the template encounters an issue, it displays an error message and/or places the category into one or more of the following tracking categories:

Maintenance required

Maintenance possible

Module maintenance possible

Tracking only

local p = {}

--[[==========================================================================]]
--[[                                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 listall = false
local tlistall = {}
local tlistallbwd = {}
local tlistallfwd = {}
local ttrackingcats = { --when reindexing, Ctrl+H 'trackcat(1,' & 'ttrackingcats[1]'
	'', -- [1] placeholder for [[Category:Navseasoncats using cat parameter]]
	'', -- [2] placeholder for [[Category:Navseasoncats using testcase parameter]]
	'', -- [3] placeholder for [[Category:Navseasoncats using unknown parameter]]
	'', -- [4] placeholder for [[Category:Navseasoncats range not using en dash]]
	'', -- [5] placeholder for [[Category:Navseasoncats range abbreviated (MOS)]]
	'', -- [6] placeholder for [[Category:Navseasoncats range redirected (base change)]]
	'', -- [7] placeholder for [[Category:Navseasoncats range redirected (end)]]
	'', -- [8] placeholder for [[Category:Navseasoncats range redirected (MOS)]]
	'', -- [9] placeholder for [[Category:Navseasoncats range redirected (other)]]
	'', --[10] placeholder for [[Category:Navseasoncats range gaps]]
	'', --[11] placeholder for [[Category:Navseasoncats range irregular]]
	'', --[12] placeholder for [[Category:Navseasoncats range irregular, 0-length]]
	'', --[13] placeholder for [[Category:Navseasoncats range ends (present)]]
	'', --[14] placeholder for [[Category:Navseasoncats range ends (blank, MOS)]]
	'', --[15] placeholder for [[Category:Navseasoncats isolated]]
	'', --[16] placeholder for [[Category:Navseasoncats default season gap size]]
	'', --[17] placeholder for [[Category:Navseasoncats decade redirected]]
	'', --[18] placeholder for [[Category:Navseasoncats year redirected (base change)]]
	'', --[19] placeholder for [[Category:Navseasoncats year redirected (var change)]] --new
	'', --[20] placeholder for [[Category:Navseasoncats year redirected (other)]]
	'', --[21] placeholder for [[Category:Navseasoncats roman numeral redirected]]
	'', --[22] placeholder for [[Category:Navseasoncats nordinal redirected]]
	'', --[23] placeholder for [[Category:Navseasoncats wordinal redirected]]
	'', --[24] placeholder for [[Category:Navseasoncats TV season redirected]]
	'', --[25] placeholder for [[Category:Navseasoncats using skip-gaps parameter]]
	'', --[26] placeholder for [[Category:Navseasoncats year and range]]
	'', --[27] placeholder for [[Category:Navseasoncats year and decade]]
	'', --[28] placeholder for [[Category:Navseasoncats decade and century]]
	'', --[29] placeholder for [[Category:Navseasoncats in mainspace]]
	'', --[30] placeholder for [[Category:Navseasoncats redirection error]]
}
local avoidself =  (not string.match(currtitle.text, 'Navseasoncats with') and
					not string.match(currtitle.text, 'Navseasoncats.*/doc') and
					not string.match(currtitle.text, 'Navseasoncats.*/sandbox') and
					currtitle.text ~= 'Navseasoncats' and 
					currtitle.nsText ~= 'User_talk' and
					currtitle.nsText ~= 'Template_talk' and
					(currtitle.nsText ~= 'Template' or testcases)) --avoid nested transclusion errors (i.e. {{Infilmdecade}})


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

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

--Failure handling
function p.failedcat( errors, sortkey )
	if avoidself then
		return (errors or '')..'&#42;&#42;&#42;Navseasoncats failed to generate navbox***'..
			   '[['..testcasecolon..'Category:Navseasoncats failed to generate navbox|'..(sortkey or 'O')..']]\n'
	end
	return ''
end

--Check for unknown parameters.
--Used by main only.
function checkforunknownparams( tbl )
	local knownparams = {
		['min'] = 'min',
		['max'] = 'max',
		['cat'] = 'cat',
		['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, 'Navseasoncats using unknown parameter')
		end
	end
end

--Tracking cat handling.
--	key: 15 (when reindexing ttrackingcats{}, Ctrl+H 'trackcat(1,' & 'ttrackingcats[1]')
--	cat: 'Navseasoncats isolated'; '' to remove
--Used by main, all nav_*(), & several utility functions.
function trackcat( key, cat )
	if avoidself and key and cat then
		if cat ~= '' then
			ttrackingcats[key] = '[['..testcasecolon..'Category:'..cat..']]'
		else
			ttrackingcats[key] = ''
		end
	end
	return
end

--Check for nav_*() navigational isolation (not necessarily an error).
--Used by all nav_*().
function isolatedcat()
	if nexistingcats == 0 then
		trackcat(15, 'Navseasoncats isolated')
	end
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 {{Category redirect}}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_*().
function catlinkfollowr( frame, cat, displaytext, displayend )
	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 grey = '#888'
	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 = mw.title.new( cat, 'Category' ).exists
	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 == 'present' 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 = '[[:Category:'..R..'|'..disp..']]'
		else
			link = '[[:Category:'..cat..'|'..disp..']]'
		end
	else
		link = '<span style="color:'..grey..'">'..disp..'</span>'
		--return { '[[:Category:'..cat..'|'..disp..']]', nil } --for debugging
	end
	
	if listall then
		if nilorR then --#R followed
			table.insert( tlistall, '[[:Category:'..cat..']] → '..'[[:Category:'..nilorR..']] ('..link..')' )
		else --no #R
			table.insert( tlistall, '[[:Category:'..cat..']] ('..link..')' )
		end
	end
	
	return {
		['cat'] = cat,
		['catexists'] = exists,
		['rtarget'] = nilorR,
		['navelement'] = link,
		['displaytext'] = disp,
	}
end

--Returns the target of {{Category redirect}}, if it exists, else returns the original cat.
--{{Title year}}, etc., if found, are evaluated.
--Used by catlinkfollowr(), and so indirectly by all nav_*().
function rtarget( frame, cat )
	local catcontent = mw.title.new( cat or '', 'Category' ):getContent()
	if string.match( catcontent or '', '{{ *[Cc]at' ) then --prelim test
		local regex = {
			--the following 11 pages (7 condensed) redirect to [[Template:Category redirect]] (as of 6/2019):
			'{{ *[Cc]ategory *[Rr]edirect', --most likely match 1st
			'{{ *[Cc]at *redirect',         --444+240 transclusions
			'{{ *[Cc]at *redir',            --8+3
			'{{ *[Cc]ategory *move',        --6
			'{{ *[Cc]at *red',              --6
			'{{ *[Cc]atr',                  --4
			'{{ *[Cc]at *move',             --0
		}
		for _, v in pairs (regex) 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(30, 'Navseasoncats redirection error')
					end
				end
				rtarget = mw.ustring.gsub(rtarget, '^1%s*=%s*', '')
				rtarget = string.gsub(rtarget, '^[Cc]ategory:', '')
				return rtarget
			end
		end --for
	end --if
	return cat
end

--Returns a numbered list of all {{Category redirect}}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_*().
function listalllinks()
	local nl = '\n# '
	local out = ''
	if currtitle.nsText == 'Category' then
		errors = p.errorclass('The <b><code>|list-all-links=yes</code></b> parameter/utility '..
							'should not be saved in category space, only previewed.')
		out = p.failedcat(errors, 'Z')
	end
	
	local bwd, fwd = '', ''
	if tlistallbwd[1] then
		bwd = '\n\nbackward search:\n# '..table.concat(tlistallbwd, nl)
	end
	if tlistallfwd[1] then
		fwd = '\n\nforward search:\n# '..table.concat(tlistallfwd, nl)
	end
	
	if tlistall[1] then
		return out..nl..table.concat(tlistall, nl)..bwd..fwd
	else
		return out..nl..'No links found!?'..bwd..fwd
	end
end

--Returns the difference b/w 2 ints separated by endash|hyphen, nil if error.
--Used by nav_hyphen() only.
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 MOS: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.
function find_terminaltxt( cat )
	local terminaltxt = nil
	if mw.ustring.match(cat, '%d+[–-]present$') then
		terminaltxt = 'present'
		trackcat(13, 'Navseasoncats range ends (present)')
	elseif mw.ustring.match(cat, '%d+[–-]$') then
		terminaltxt = ''
		trackcat(14, 'Navseasoncats range ends (blank, MOS)')
	end
	return terminaltxt
end

--Returns an unsigned string of the 1-4 digit decade ending in "0", else nil.
--Used by nav_decade() only.
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.
function defaultgapcat( bool )
	if bool and nexistingcats == 0 then
		--using "nexistingcats > 0" isn't as useful, since the default gap size obviously worked
		trackcat(16, 'Navseasoncats default season gap size')
	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..'th' end
		
		local  ones = string.match(s, '%d$')
		if     ones == '1' then return s..'st'
		elseif ones == '2' then return s..'nd'
		elseif ones == '3' then return s..'rd' end
		
		return s..'th'
	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.
function navcenter( i, catlink )
	if i == 0 then --center nav element
		if navborder == true then
			return '*<b>'..catlink.displaytext..'</b>\n'
		else
			return '*<b>'..catlink.navelement..'</b>\n'
		end
	else
		return '*'..catlink.navelement..'\n'
	end
end

--Return conditionally aligned stacked navs.
--Used by main only.
function nav1nav2( nav1, nav2 )
	if avoidself then
		local forcealign = '<div style="display:block !important; max-width: calc(100% - 25em);">'
		return forcealign..'\n'..nav1..'\n'..nav2..'\n</div>'
	else
		return nav1..'\n'..nav2
	end
end


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


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

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('Function nav_hyphen can\'t recognize the number "'..(start or '')..'" '..
								  'in the first part of the "season" that was passed to it. '..
								  'For e.g. "2015–16", "2015" is expected via "|2015|–|16|".')
			return p.failedcat(errors, 'H')
		end
	end
	local nstart = tonumber(start)
	
	--en dash check
	if hyph ~= '–' then
		trackcat(4, 'Navseasoncats range not using 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 }
	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(13, 'Navseasoncats range ends (present)')
		else				 trackcat(14, 'Navseasoncats range ends (blank, MOS)') end
	elseif (start == finish) and
		   (ttrackingcats[15] ~= '') --nav_year found isolated; check for surrounding hyphenated terms (e.g. UK MPs 1974)
	then
		trackcat(15, '') --reset for another check later
		trackcat(12, 'Navseasoncats range irregular, 0-length')
		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('Function nav_hyphen can\'t recognize "'..(finish or '')..'" '..
								  'in the second part of the "season" that was passed to it. '..
								  'For e.g. "2015–16", "16" is expected via "|2015|–|16|".')
			return p.failedcat(errors, 'I')
		end
	else
		if string.len(finish) >= 5 then
			errors = p.errorclass('The second part of the season passed to function nav_hyphen should only be four or fewer digits, not "'..(finish or '')..'". '..
								  'See [[MOS:DATERANGE]] for details.')
			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 term_limit = 10
	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('Function nav_hyphen can\'t determine a reasonable term length for "'..start..hyph..finish..'".')
			return p.failedcat(errors, 'K')
		end
		t = t + 1
	end
	
	--apply MOS: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('The second part of the season passed to function nav_hyphen should be two or four digits, not "'..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, 'Navseasoncats range abbreviated (MOS)')
			elseif lenfinish ~= 4 then
				errors = p.errorclass('The second part of the season passed to function nav_hyphen should be four digits, not "'..finish..'".')
				return p.failedcat(errors, 'M')
			end
		end
		if finish == '00' then --full year required regardless of term length
			trackcat(5, 'Navseasoncats range abbreviated (MOS)')
		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   = 6 --less expensive per-increment (inc x 4)
	local hgap_limit_irreg = 6 --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 mw.title.new(prevseason2, 'Category').exists or --use 'or', in case we're at the edge of the cat structure,
			   mw.title.new(nextseason2, 'Category').exists or --or we hit a "–00"/"–2000" situation on one side
			   mw.title.new(prevseason4, 'Category').exists or
			   mw.title.new(nextseason4, 'Category').exists
			then
				hgap_success = true
				break
			end
		elseif t > 1 then --test full range first, then abbreviated range, to be frugal with expensive functions
			if mw.title.new(prevseason4, 'Category').exists or --use 'or', in case we're at the edge of the cat structure,
			   mw.title.new(nextseason4, 'Category').exists or --or we hit a "–00"/"–2000" situation on one side
			   mw.title.new(prevseason2, 'Category').exists or 
			   mw.title.new(nextseason2, 'Category').exists
			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, MOS:DATERANGE-violating cats are ignored;
	--an irregular-term-length series should follow "YYYY..hyph..YYYY" throughout
	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 = -3 --pseudo nav position & index of tirregs[] for j > 0
		while j <= 3 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
							   (mw.title.new( full, 'Category' ).exists == false)
							then --allow bare-bones MOS: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 mw.title.new( full, 'Category' ).exists then
								if to == '0-length' then
									trackcat(12, 'Navseasoncats range irregular, 0-length')
								end
								tlistallbwd[#tlistallbwd] = spanblue..tlistallbwd[#tlistallbwd]..span..' (found)'
								ttlens[ find_duration(full) ] = 1
								tgaps[g] = 1
								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 > 3 then --lest we keep searching & finding 0-length cats ("MEPs for the Republic of Ireland 1973" & down)
										gbreak = true
										break
									end
								end
							end
						end --ghetto "continue"
						k = k + 1
						lastk = k
					end --while k
					if gbreak == true then break end
					g = g + 1
					lastg = g
				end --while g
			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
							   (mw.title.new( full, 'Category' ).exists == false)
							then --allow bare-bones MOS: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 mw.title.new( full, 'Category' ).exists then
								if to4 == '0-length' then
									if rtarget(frame, full) == full then --only use 0-length cats that don't #R
										trackcat(12, 'Navseasoncats range irregular, 0-length')
									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
									tgaps[g] = 1
									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 > 3 then --lest we keep searching & finding 0-length cats ("2018 CONCACAF Champions League" & up)
											gbreak = true
											break
										end
									end
								end
							end
						end --ghetto "continue"
						k = k + 1
						lastk = k
					end --while k
					if gbreak == true then break end
					g = g + 1
					lastg = g
				end --while g
			end --if j > 0
			
			if (lastg == (hgap_limit_irreg + 1)) and 
			   (lastk == (term_limit + 1))
			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 <= 3
	end --if hgap <= hgap_limit_reg
	
	--begin navhyphen
	local navh = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local terminalcat = false --switch used to hide future cats
	local terminaltxt = nil
	local i = -3 --nav position
	while i <= 3 do
		local from = nstart + i*(t+hgap) --the logical, but not necessarily correct, 'from'
		if tirregs['from'..i] then from = tonumber(tirregs['from'..i]) end --prefer irregular term table
		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 MOS:DATERANGE (e.g. 1999-2004)
		  (from2 - (to2 or from2)) > 0 --century transition exception (e.g. 1999–2000)
		then
			tofinal = (to or '')       --default to the MOS-correct format, in case no fallbacks found
		end
		if to == '0-length' then
			tofinal = to
		end
		
		--check existance of 4-digit, MOS-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 mw.title.new( full, 'Category' ).exists then
					local abbr = firstpart..lspace..from..hyph..to2..tspace..lastpart
					if mw.title.new( abbr, 'Category' ).exists then
						tofinal = (to2 or '') --rv to MOS-incorrect format; if full AND abbr DNE, then tofinal is still in its MOS-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 mw.title.new( abbr, 'Category' ).exists and tofinal ~= to then
					local full = firstpart..lspace..from..hyph..to..tspace..lastpart
					if mw.title.new( full, 'Category' ).exists 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 {{Category redirect}} was followed, figure out why
				--determine new term length & gap size
				ttlens[ find_duration( catlink.rtarget ) ] = 1
				if i > -3 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,
						tgaps[ gap ] = 1						--tgaps[-1] is ignored
					end
				end
				
				--display/tracking handling
				local base_regex = '%d+[–-]%d+'
				local origbase = mw.ustring.gsub(orig, base_regex, '')
				local rtarbase = mw.ustring.gsub(catlink.rtarget, base_regex, '')
				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, 'Navseasoncats range redirected (base change)')
				elseif terminalcat == 1 then
					trackcat(7, 'Navseasoncats range redirected (end)')
				else
					local all4s_regex = '%d%d%d%d[–-]%d%d%d%d'
					local all4s = (mw.ustring.match(orig, all4s_regex) and
								   mw.ustring.match(catlink.rtarget, all4s_regex))
					if all4s then
						trackcat(9, 'Navseasoncats range redirected (other)')
					else
						trackcat(8, 'Navseasoncats range redirected (MOS)')
					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
				navh = navh..'*'..catlink.navelement..'\n'
				if terminalcat then nmaxseas = nminseas_default end --prevent display of future ranges
			else
				local hidden = '<span style="visibility:hidden">'..disp..'</span>'
				navh = navh..'*'..hidden..'\n'
				if listall then
					tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
				end
			end
		else --center navh
			if finish == -1 then finish = 'present'
			elseif finish == 0 then finish = '<span style="visibility:hidden">'..start..'</span>' end
			local disp = start..hyph..finish
			if regularparent == 'isolated' then disp = start end
			navh = navh..'*<b>'..disp..'</b>\n'
		end
		
		i = i + 1
	end
	
	--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
		for s = 0, term_limit do
			itlens = itlens + (ttlens[s] or 0)
		end
		if igaps  > 0 then trackcat(10, 'Navseasoncats range gaps') end
		if itlens > 1 and ttrackingcats[12] == '' then --avoid duplication in "Navseasoncats range irregular, 0-length"
			trackcat(11, 'Navseasoncats range irregular')
		end
	end
	isolatedcat()
	defaultgapcat(not hgap_success)
	if listall then
		return listalllinks()
	else
		return navh..'|}'
	end
end


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

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('Function nav_tvseason can\'t recognize the TV season number sent to its 2nd parameter.')
		return p.failedcat(errors, 'T')
	end
	
	local maxtv = tonumber(maximumtv) or 9999 --allow +/- qualifier
	if maxtv < tv then maxtv = tv end --input error; maxtv should be >= parent
	
	--begin navtvseason
	local navt = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	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..lastpart, t )
			if (t >= 1 and t <= maxtv) then --hardcode mintv
				if catlink.rtarget then --a {{Category redirect}} was followed
					trackcat(24, 'Navseasoncats TV season redirected')
				end
				navt = navt..'*'..catlink.navelement..'\n'
			else
				local hidden = '<span style="visibility:hidden">'..'0'..'</span>' --'0' to maintain dot spacing
				navt = navt..'*'..hidden..'\n'
				if listall then
					tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
				end
			end
		else --center navt
			navt = navt..'*<b>'..tv..'</b>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navt..'|}'
	end
end


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

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('Function nav_decade was sent "'..(decade or '')..'" as its 2nd parameter, '..
							'but expects a 1 to 4-digit year ending in "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, 'BC')
		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('Function nav_decade was sent "'..(mindecade or '')..'" as its 4th parameter, '..
							'but expects a 1 to 4-digit year ending in "0", the earliest decade to be shown.')
		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, 'BC')
		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('Function nav_decade was sent "'..(maxdecade or '')..'" as its 5th parameter, '..
							'but expects a 1 to 4-digit year ending in "0", the highest decade to be shown.')
		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, '^BC') --following the "0s BC" convention for all years BC
	lastpart = mw.ustring.gsub(lastpart, '^BC%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 Navseasoncats year and decade
		bnb = ' border-style: none; background-color: transparent;'
	end
	local navd = '{| class="toccolours hlist" style="text-align: center; margin: auto;'..bnb..'"\n'..'|\n'
	
	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 = 'BC '
				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 = 'BC '
				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 = ' BC' --show BC for all BC decades whenever a "0s" is displayed on the nav
		end
		
		--determine target cat
		local disp = d..'s'..BCdisp
		local catlink = catlinkfollowr( frame, firstpart..' '..d..'s'..tspace..BC..lastpart, disp )
		if catlink.rtarget then --a {{Category redirect}} was followed
			trackcat(17, 'Navseasoncats decade redirected')
		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
					navd = navd..shown
					hidden = nil
				else
					navd = navd..'*'..hidden..'\n'
				end
			else
				navd = navd..shown --the common case
				hidden = nil
			end
		else
			navd = navd..'*'..hidden..'\n'
		end
		if listall and hidden then
			tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
		end
		
		i = i + 10
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navd..'|}'
	end
end


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

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 '', 'BC') then minyear = -math.abs(minyear) end --allow BC qualifier (AD otherwise assumed)
	if string.match(maximumyear or '', 'BC') then maxyear = -math.abs(maxyear) end --allow BC qualifier (AD otherwise assumed)
	
	if year == nil then
		errors = p.errorclass('Function nav_year can\'t recognize the year sent to its 2nd parameter.')
		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 = string.match(firstpart, 'AD$')  --following the "AD 1" convention from AD 1 to AD 10
	local parentBC = string.match(lastpart, '^BCE?') --following the "1 BC" convention for all years BC
	firstpart = mw.ustring.gsub(firstpart, '%s*AD$', '') --handle AD/BC separately for easier & faster accounting
	lastpart  = mw.ustring.gsub(lastpart,  '^BCE?%s*', '')
	local BCe = parentBC or yearBCElastparts[lastpart] or 'BC' --"BC" 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 <= 5 do --Czech Republic, Poland, Sri Lanka, etc. have 5-year terms
			prevseason = firstpart..lspace..(year-ygap1)..tspace..lastpart
			if mw.title.new(prevseason, 'Category').exists then
				ygap1_success = true
				break
			end
			ygap1 = ygap1 + 1
		end
		
		local nextseason = nil
		while ygap2 <= 5 do --Czech Republic, Poland, Sri Lanka, etc. have 5-year terms
			nextseason = firstpart..lspace..(year+ygap2)..tspace..lastpart
			if mw.title.new(nextseason, 'Category').exists 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)]
	local skipgaps_limit = 25
	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 = mw.title.new( cat, 'Category' ).exists
						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 = mw.title.new( cat, 'Category' ).exists
						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 --AD/BC not supported
		end
	end
	
	--begin navyears
	local navy = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local y
	local i = -5 --nav position
	while i <= 5 do
		if skipgaps then
			y = ynogaps[i]
		else
			y = year + i*ygap*switchADBC
		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 = '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 = '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 = 'AD '
				end
			end
			if BC ~= '' and year <= 5 then --only show 'BC' 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)'
					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, MOS-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(26, 'Navseasoncats year and range')
					else
						if listall then
							tlistall[#tlistall] = tlistall[#tlistall]..' (tried; not displayed)'
						end
						local yHyph_2 = y..'–'..string.match(y+1, '%d%d$') --try 2010–11 type cats
						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(26, 'Navseasoncats year and range')
						elseif listall then
							tlistall[#tlistall] = tlistall[#tlistall]..' (tried; not displayed)'
						end
					end
				end
				if catlink.rtarget then --#R followed; determine why
					local r = catlink.rtarget
					local c = catlink.cat
					local regex_year  = '%d%d%d%d[–-]?%d?%d?%d?%d?' --prioritize year/range stripping, e.g. for "2006 Super 14 season"
					local regex_num   = '%d+' --strip any number otherwise
					local regex_final = nil   --best choice goes here
					if string.match(r, regex_year) and string.match(c, regex_year) then
						regex_final = regex_year
					elseif string.match(r, regex_num) and string.match(c, regex_num) then
						regex_final = regex_num
					end
					if regex_final then
						local r_base = mw.ustring.gsub(r, regex_final, '')
						local c_base = mw.ustring.gsub(c, regex_final, '')
						if r_base ~= c_base then
							trackcat(18, 'Navseasoncats year redirected (base change)') --acceptable #Rs go here
						else
							trackcat(20, 'Navseasoncats year redirected (other)')  --exceptions go here
						end
					else
						trackcat(19, 'Navseasoncats year redirected (var change)') --e.g. "V2 engines" to "V-twin engines"
					end
				end
				navy = navy..'*'..catlink.navelement..'\n'
			else --OOB vs min/max
				local hidden = '<span style="visibility:hidden">'..disp..'</span>'
				navy = navy..'*'..hidden..'\n'
				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
			navy = navy..'*<b>'..year..BCdisp..'</b>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navy..'|}'
	end
end


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

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('Function nav_roman can\'t recognize one or more of "'..(num or 'nil')..'" & "'..
							(rom or 'nil')..'" in category "'..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 = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	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 {{Category redirect}} was followed
						trackcat(21, 'Navseasoncats roman numeral redirected')
					end
					navr = navr..'*'..catlink.navelement..'\n'
				else
					local hidden = '<span style="visibility:hidden">'..r..'</span>'
					navr = navr..'*'..hidden..'\n'
					if listall then
						tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
					end
				end
			else --center navr
				navr = navr..'*<b>'..r..'</b>\n'
			end
		else
			navr = navr..'*<span style="visibility:hidden">'..'I'..'</span>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navr..'|}'
	end
end


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

function nav_nordinal( frame, firstpart, ord, lastpart, minimumord, maximumord )
	local nord = tonumber(ord)
	local minord = tonumber(string.match(minimumord or '', '(-?%d+)[snrt]?[tdh]?')) or -9999 --allow full ord & +/- qualifier
	local maxord = tonumber(string.match(maximumord or '', '(-?%d+)[snrt]?[tdh]?')) or  9999 --allow full ord & +/- qualifier
	if string.match(minimumord or '', 'BC') then minord = -math.abs(minord) end --allow BC qualifier (AD otherwise assumed)
	if string.match(maximumord or '', 'BC') then maxord = -math.abs(maxord) end --allow BC qualifier (AD otherwise assumed)
	
	local temporal = string.match(lastpart, 'century') or
					 string.match(lastpart, 'millennium')
	
	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'] = 'BCE', --WP:CFD/Log/2016 June 21#Category:11th-century BC Hebrew people
		['-century Jews']          = 'BCE', --co-nominated
		['-century Judaism']       = 'BCE', --co-nominated
		['-century rabbis']        = 'BCE', --co-nominated
		['-century High Priests of Israel'] = 'BCE',
	}
	local parentBC = mw.ustring.match(lastpart, '%s(BCE?)')       --"1st-century BC" format
	local lastpartNoBC = mw.ustring.gsub(lastpart, '%sBCE?', '')  --easier than splitting lastpart up in 2; AD never used
	local BCe = parentBC or ordBCElastparts[lastpartNoBC] or 'BC' --"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 Navseasoncats decade and century
		bnb = ' border-style: none; background-color: transparent;'
	end
	local navo = '{| class="toccolours hlist" style="text-align: center; margin: auto;'..bnb..'"\n'..'|\n'
	
	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 'BC' 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 {{Category redirect}} was followed
					trackcat(22, 'Navseasoncats nordinal redirected')
				end
				navo = navo..navcenter(i, catlink)
			else
				navo = navo..'*'..hidden..'\n'
				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 {{Category redirect}} was followed
				trackcat(22, 'Navseasoncats nordinal redirected')
			end
			navo = navo..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
			navo = navo..'*'..hidden..'\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navo..'|}'
	end
end


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

function nav_wordinal( frame, firstpart, word, lastpart, minimumword, maximumword, ordinal, frame )
	--Module:ConvertNumeric.numeral_to_english() flags:
	--   ordinal == 'on': 'second' is output instead of 'two'
	--   ordinal ~= 'on': 'two' is output instead of 'second'
	local ord2eng = require('Module:ConvertNumeric').numeral_to_english
	local eng2ord = require('Module:ConvertNumeric').english_to_ordinal
	local th = 'th'
	if ordinal ~= 'on' then
		th = ''
		eng2ord = require('Module:ConvertNumeric').english_to_numeral
	end
	local sc = string.match(word, '^%u') --sentence-case check
	local lc = string.lower(word) --operate on/with lc, and restore any sc later
	local nord = eng2ord(lc)
	local case = nil
	if sc then case = 'U' 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 "Straight-eight engines"-type cats
	if string.match(lastpart, '^[%-%)]' ) then tspace = '' end --DNE for "Nine-cylinder engines"-type cats
	
	--sterilize min/max
	local minword = 1
	local maxword = 99
	if minimumword then
		local num = tonumber(minimumword)
		if num and 0 < num and num < maxword then
			minword = num
		else
			local ord = eng2ord(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 = eng2ord(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
	
	--begin navwordinal
	local navw = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local i = -5 --nav position
	while i <= 5 do
		local n = nord + i
		
		if n >= 1 then
			local nth = p.addord(n)
			if ordinal ~= 'on' then nth = n end
			if i ~= 0 then --left/right navw
				local frame_args = frame:newChild{ args = { n, ord = ordinal, case = case } } --easier to do this than modify Module:ConvertNumeric
				local w = ord2eng( frame_args )
				local catlink = catlinkfollowr( frame, firstpart..lspace..w..tspace..lastpart, nth )
				if minword <= n and n <= maxword then
					if catlink.rtarget then --a {{Category redirect}} was followed
						trackcat(23, 'Navseasoncats wordinal redirected')
					end
					navw = navw..'*'..catlink.navelement..'\n'
				else
					local hidden = '<span style="visibility:hidden">'..nth..'</span>'
					navw = navw..'*'..hidden..'\n'
					if listall then
						tlistall[#tlistall] = tlistall[#tlistall]..' ('..hidden..')'
					end
				end
			else --center navw
				navw = navw..'*<b>'..nth..'</b>\n'
			end
		else
			navw = navw..'*<span style="visibility:hidden">'..'0'..th..'</span>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navw..'|}'
	end
end


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

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 = 'Category:'..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+[–-])$') or --irreg; ending unknown, e.g. "Members of the Scottish Parliament 2021–"
					 mw.ustring.match(cpagename, '%s(%d+[–-]present)$') --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, 'season (%d+)') or
					 mw.ustring.match(cpagename, 'series (%d+)')
					
	local nordinal = mw.ustring.match(cpagename, '[:%s](%d+[snrt][tdh])[-%s]') or
					 mw.ustring.match(cpagename, '[:%s](%d+[snrt][tdh])$')
					
	local decade   = mw.ustring.match(cpagename, '[:%s](%d+s)[%s-]') or
					 mw.ustring.match(cpagename, '[:%s](%d+s)$')
					
	local year     = mw.ustring.match(cpagename, '[:%s](%d%d%d%d)%s') or --prioritize 4-digit years
					 mw.ustring.match(cpagename, '[:%s](%d%d%d%d)$') or
					 mw.ustring.match(cpagename, '[:%s](%d+)%s') or
					 mw.ustring.match(cpagename, '[:%s](%d+)$') 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/least 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
			if nordinal then return { ['vtype'] = 'nordinal', ['v'] = nordinal } end
			if decade   then return { ['vtype'] = 'decade',   ['v'] = decade   } end
			if year     then return { ['vtype'] = 'year',     ['v'] = year     } end
			if roman    then return { ['vtype'] = 'roman',    ['v'] = roman    } end
		end
	else
		--try wordinals ('zeroth' to 'ninety-ninth' only)
		local eng2ord = require('Module:ConvertNumeric').english_to_ordinal
		local split = mw.text.split(pagename, ' ')
		for i=1, #split do
			if eng2ord(split[i]) > -1 then
				return { ['vtype'] = 'wordinal', ['v'] = split[i] }
			end
		end
		
		--try English numerics ('one'/'single' to 'ninety-nine' only)
		local eng2num = require('Module:ConvertNumeric').english_to_numeral
		local split = mw.text.split(pagename, '[%s%-]') --e.g. "Nine-cylinder engines"
		for i=1, #split do
			if eng2num(split[i]) > -1 then
				return { ['vtype'] = 'enumeric', ['v'] = split[i] }
			end
		end
	end
	
	errors = p.errorclass('Function find_var can\'t find the variable text in category "'..pagename..'".')
	return { ['vtype'] = 'error', ['v'] = p.failedcat(errors, 'V') }
end


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

function p.navseasoncats( 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']
	
	--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(25, 'Navseasoncats using skip-gaps parameter')
	end
	
	--ns checks
	if currtitle.nsText == 'Category' then
		if cat and cat ~= '' then
			trackcat(1, 'Navseasoncats using cat parameter')
		end
		if testcase and testcase ~= '' then
			trackcat(2, 'Navseasoncats using testcase parameter')
		end
	elseif currtitle.nsText == '' then
		trackcat(29, 'Navseasoncats in mainspace')
	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
		if firstpart_dec ~= '' then
			firstpart_dec = firstpart_dec..' the'
		elseif firstpart_dec == 'AD' and dec <= 1 then
			firstpart_dec = ''
			if dec == 0 then dec = '' end
		end
		local decade = dec..'0s '
		decadecat = mw.text.trim( firstpart_dec..' '..decade..lastpart )
		local exists = mw.title.new( decadecat, 'Category' ).exists
		if exists then
			navborder = false
			trackcat(27, 'Navseasoncats year and decade')
			local nav2 = nav_decade( frame, firstpart_dec, decade, lastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats)
			return nav1nav2( nav1, nav2 )
		elseif ttrackingcats[15] ~= '' then --nav_year isolated; check nav_hyphen (e.g. UK MPs 1974, Moldovan MPs 2009, etc.)
			hyphen = '–'
			finish = start
			local nav2 = nav_hyphen( frame, start, hyphen, finish, firstpart, lastpart, minimum, maximum, testcasegap )..testcaseindent..table.concat(ttrackingcats)
			if ttrackingcats[15] ~= '' then return nav1 --still isolated; rv to nav_year
			else return nav2 end
		else --regular nav_year
			return 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+)s'))
		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
		local clastpart = ' century '..lastpart
		local centurycat = mw.text.trim( firstpart..' '..p.addord(century)..clastpart )
		local exists = mw.title.new( centurycat, 'Category' ).exists
		if not exists then --check for hyphenated century
			clastpart = '-century '..lastpart
			centurycat = mw.text.trim( firstpart..' '..p.addord(century)..clastpart )
			exists = mw.title.new( centurycat, 'Category' ).exists
		end
		if exists then
			navborder = false
			trackcat(28, 'Navseasoncats decade and century')
			local nav2 = nav_nordinal( frame, firstpart, century, clastpart, minimum, maximum )..testcaseindent..table.concat(ttrackingcats)
			return nav1nav2( nav1, nav2 )
		else
			return nav1
		end
		
	elseif findvar.vtype == 'nordinal' then --e.g. "1st", "99th"; ~7.5% of cats
		return 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 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 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 = 'on'
		return 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 = 'off'
		return 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 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([–-])present$'), -1 --ascii 150 & 45 (ndash & keyboard hyphen); mw req'd
		if hyphen == nil then
			hyphen, finish = mw.ustring.match(findvar.v, '%d([–-])$'), 0 --0/-1 are hardcoded switches for nav_hyphen()
		end
		return nav_hyphen( frame, start, hyphen, finish, firstpart, lastpart, minimum, maximum, testcasegap )..testcaseindent..table.concat(ttrackingcats)
		
	else                                 --malformed
		errors = p.errorclass('Failed to determine the appropriate nav function from malformed season "'..findvar.v..'". ')
		return p.failedcat(errors, 'N')..table.concat(ttrackingcats)
	end
end

return p