This Module was written by Alexander Zhikun He, also known as, User:Codehydro on the English Wikipedia

All methods were developed independently and any resemblance to other string buffer libraries would be coincidental.
Furthermore, many methods will not work when compiled by standard Lua libraries as they depend on behaviors unique to
the MediaMiki Scribunto mod, which, for example, has a getmetatable method that always returns nil on non-tables.
https://www.mediawiki.org/wiki/Extension:Scribunto/Lua_reference_manual

Source code comments may be thin at some points because they are intended to be supplemented by the documentation page:
https://en.wikipedia.org/wiki/Module:Buffer/doc

Licensed under Creative Commons Attribution-ShareAlike 3.0 Unported License
https://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License

https://en.wikipedia.org/wiki/Module:Buffer
https://en.wikipedia.org/wiki/User:Codehydro

############## --]]
local function Valid(v)--type validation
	if v and v~=true then--reject nil/boolean; faster than 2 type comparisons
		local str = tostring(v)--functions not filtered since unlikely passed by accident (Scribunto does not have userdata/thread types)
		if str~=v and str=='table' then return rawget and table.concat(v) end--tostring(string-type) returns same ref; same refs compare faster than type
		if str~='' then return str end--numbers are coerced to string per table.concat op; appending in string form saves ops on repeat concat
	end
end
local noOp, MBpairs = functionend do local iMap, vMap, oMap, pIter, pOther, pFast, Next--Map
	local function init--init = noOp after first run
		function Next(t) return next, t end--slightly faster to do this than to use select
		function pIter k = (iMap[t] or MBpairs and iMap[t])[not k and 1 or vMap[t][k]] return k, t[k] end--don't use rawget; accepting unmapped tables does not measurably affect performance.
		function pOther k = (oMap[t] or MBpairs and oMap[t])[nil==k and 1 or vMap[t][k]] return k, t[k] end--comparison to nil because false is a valid key
		function pFast k = not k and 1 or k < (vMap[t] or #t) and k + 1 or nil return k, t[k] end--mapless iterator; almost as fast as native ipairs; slight performance penalty when length not cached
							 --k and k < (vMap[t] or #t) and k + 1 or not k and 1 or nil return k, t[k] end--mapless iterator; almost as fast as native ipairs; slight performance penalty when length not cached
		local mk = {__mode = 'k'}--use mode 'k'; found that mode 'kv' sometimes garbage collects maps mid-loop 
		init, iMap, vMap, oMap = noOp, setmetatable, setmetatable, setmetatable--iMap is numeric keys, oMap is non-numeric keys, and vMap points to next key
	end
	function MBpairs--pairs always iterates in order
		local iter, ex = ...
		iter = iter==init--nil
		if iter and not oMap[t] and ex==nil and rawget~=nil and next==nil then--while possible to miss keys, more thorough check would negate the benefit of pFast
			vMap[t] = #t return pFast, t, nil
		elseif ... or not vMap[t] or select~=1 then
			local ti, tn, to, n = {}, {}, {}, #t--reduces table lookups
			iMap[t], vMap[t], oMap[t] = ti, tn, to
			for k = 1, n do ti[k], tn[k] = k, k + 1 end--stage one avoids number type checking op in stage two for most numeric keys
			for k in (ex or Next)(t) do
				if not tn[k] then table.insert(tonumber(k)~=k and to or ti, k) end
			end
			if #ti~=n then
				table.sort(ti)
				for k = 1, #ti do tn[ti[k]] = k + 1 end--somewhat wasteful, but trying to avoid overwriting can be even more expensive
			end
			for k = 1, #to do tn[to[k]] = k + 1 end
		end
		return iter and pIter or oMap[t] and pOther or noOp, t--noOp for mapless
	end
end
local parent, rawkey, spec do--new scope for variables not reused outside (reduces number of var names that need to checked outside of scope)
	local mkv = {__mode='kv', __call=functiont[k]=v return k end}--shared meta for Buffer parent property, raw mode, and specialized functions
	parent, rawkey, spec = setmetatable, setmetatable, setmetatable--shared meta less memory
end

local MB, MBi, MBmix, buffHTML, gfuncs, noCache, Element do--minimize number of locals per scope to reduce time spent sifting through irrelevant variable names
	local _stream do local stream--keep stream near top of scope
		local function init(f)--init = noOp after first run
			local function each
				for k = 1, select do
					k = Valid(select)--slightly faster than table.insert(self, (Valid(select)))
					if k then table.insert end
				end
				return self
			end
			init, stream, _stream = noOp, {
				__call = function v = v and Valid(v) return v and table.insert or t end,--last_concat cleared before entering stream mode
				__index = function return i=='each' and each or MB.__index and setmetatable[i] end,--no table look up minimizes resources to retrieve the only stream function
				__tostring = function(t) return setmetatable end
			setmetatable(stream, getmetatable(MB))
		end
		function _stream self.last_concat = init return setmetatable:each(...) end
	end
	local function isMBfunc--helper for :getParent-like methods (including getBuffer which does not return a parent)
		return s and (select==0 and--eventually should figure out to make this work for :getHTML which is very similar
				(not rawkey[s] and tostring(s):match'^_.*' and MB.__index and MB.__index(Buffer) or MBmix)--unprefixed function names append as a string
				or assert(MB.__index, ('" %s " does not match any available Module:Buffer function'):format(s))--getParent is a one-way trip so one-time assert not expensive
			) or Buffer
	end
	local function MBselect--helper for :_out and :_str
		local n, seps = n - 1, {select}
		if type(seps[n])=='table' then 
			if buffHTML and rawget then return ... end
			setmetatable(seps, {__index = setmetatable(seps[n], {__index = function(t) return rawget end})})[n] = nil
		end
		return ..., seps
	end
	local _inHTML do local lastBuffer, lastHTML
		local function init(...)--init replaced and new version called on return
			local create, mwFunc = mw.html.create do
				local mwHTMLmeta = getmetatable(create)
				buffHTML, mwFunc, _inHTML = setmetatable(mw.clone(mwHTMLmeta), getmetatable(MB)), mwHTMLmeta.__index--buffHTML declared near top of module; remove _inHTML from outer scope
				function init
					local name, args, tag = select(... and type(...)=='table' and 1 or 2, nil, ...)
					tag = create(Valid(name), args)
					if nodes then table.insert(nodes, tag.parent and tag or rawset) end
					if args then
						local a, b = args.selfClosing, args.parent
						args.selfClosing, args.parent = nil
						if next(args) then Element._add(parent, args) end
						args.selfClosing, args.parent = a, b--in case args is reused
					end
					return tag
				end
				for k, v in next, {[mw] = mwHTMLmeta,
					__call = function return MBmix(spec[h.nodes] and h.nodes or spec(setmetatable(parent, MB), Element), v) end,
					__concat = false,--false means take from MB
					__eq = false
			end
			local nonSelf, BHi = {tag=true,done=true,allDone=true}, buffHTML.__index do local g
				g = {__index = function
					if gfuncs and gfuncs[i] then g.__index, gfuncs = gfuncs return g.__index[i] end
				end}
				setmetatable
				setmetatable
			end
			for k in next, nonSelf do--any HTML objects returned by these funcs will be granted Module:Buffer enhancements
				local func = mwFunc[k]
				BHi[k] = function local HTML = func return parent[HTML] and HTML or setmetatable(parent, buffHTML) end
			end
			do local function joinNode
					local nodes, join = HTML.nodes
					if noCache and rawkey[sep] or Valid(sep) then join, HTML.nodes = tostring(rawset(HTML, 'nodes', {MB.__call})), nodes end
					return join or tostring(HTML)
				end
				for k, v in next, {
					getParent = function lastHTML = HTML return MBi.getParent end,--return to Buffer that created the HTML tree
					getBuffer = function lastHTML = HTML return isMBfunc end,--return to last used
					killParent = function MBi.killParent return HTML end,
					_out = function
						if ...==0 then MBi._out return HTML end
						lastHTML, HTML = HTML, HTML:allDone
						local n, ops, seps = select
						if n > 1 then
							local ops, seps = MBselect
							return parent[HTML]:_in(joinNode(HTML, rawget)):_out(ops, rawset)
						end
						return parent[HTML]:_(joinNode)
					end,
					_str = function--does not set lastHTML
						if ...==0 then return joinNode(HTML, select) end--passing 0 strings without calling allDone
						local HTML, n = HTML:allDone, select
						if n > 1 then
							local ops, seps = MBselect
							return parent[HTML]:_in(joinNode(HTML, rawget)):_str(ops, rawset)
						end
						return joinNode
					end,
					_parent = function table.insert(HTML.nodes, parent[HTML:allDone]:_str(...)) return HTML end
			end
			do local htmlArg, skip, outFuncs = {parent=true,selfClosing=true,tagName=true}, {}
				do local out local function func return out end
					outFuncs = setmetatable({
						tag = function return parent(setmetatable(init, buffHTML), parent[nodes]) end,
						done = function
							b = parent[b] 
							while b.parent and ops~=0 do b, ops = b.parent, ops and ops - 1 or 0 end
							return b
						end
						if rawget then out = BHi[i] return func end--rawget to exclude globals
					end})
				end
				Element = {
					_add = function
						for k, v in MBpairs(t), t, skip[t] do (v~=true and MBmix or noOp) end
						local HTML = parent[nodes] for k, v in MBpairs do
							if htmlArg[k] then HTML[k] = v
							elseif v and v~=true then
								if nonSelf[k] then
									if k=='tag' then
										if type(v)=='table' then
											skip[v], k = 1, rawset(create(Valid(v[1])), 'parent', HTML)
											Element._add(spec(parent(k.nodes, k, table.insert), Element), v)
											if k.selfClosing then k.nodes = nil else spec[k.nodes], parent[k.nodes] = nil end--free memory/reduce clutter; parent ref will auto-unset when k.nodes is nil
											if not k.tagName then k.styles, k.attributes = nil end
										else table.insert(nodes, create(v)) end
									elseif mwFunc[k] then
										if k=='done' and tonumber(v)~=v and v[1] and tonumber(v[1])==v[1] then skip[v] = 1 end
										MBmix(outFuncs[k].nodes, v)
									elseif v[1] or v[2] then
										k = MBi[k](nodes, unpack(v, 1, rawset[v]))
										Element._add(getmetatable(k) and rawget or k, v)--if k is not a table, then v should not contain any extra keys or this may error.
									else MBi[k] end--k probably == '_G' or '_R'
								elseif mwFunc[k] then
									if type(v)~='table' or rawget then mwFunc[k]
									else
										local css = k=='css'
										for x, y in MBpairs do (y and y~=true and mwFunc[k] or noOp)(HTML, css and x:gsub or x, y) end--iterate non-numbers first
										for _, y in MBpairs do (y and y~=true and mwFunc[k] or noOp) end--don't bother with gsub since text must be quoted anyhow
									end
								elseif rawget or rawget then
									if tonumber(v)==v or v[1]==nil or getmetatable(v) then (Element[k] or MBi[k])--v is probably string-able object, or a table to be handled by :_all
									else (Element[k] or MBi[k])(nodes, unpack(v, 1, table.maxn(v))) end--v is definately a table
								else mwFunc.css(HTML, k:gsub, tostring(v)) end--oddly enough, :_add clocked its fastest runtime after adding auto-gsub as a feature
								skip[v] = nil
							end
						end
						return nodes
					end
				local tempMeta = {mode='v', copy={styles=true,attributes=true}}
				function tempMeta.__index return tempMeta.copy[i] and rawset(t, i, MBi._cc)[i] or t.orig[i] end
				rawkey[setmetatable(Element, {__index = outFuncs, __concat=function return setmetatable({nodes=spec,orig=parent[v]}, tempMeta) end})] = math.huge
			end
			function MBi:getHTML(...)
				lastBuffer = self
				if ... then
					if select==1 then return not rawkey[s] and tostring(...):match'^_' and BHi[...] and BHi[...](lastHTML) or lastHTML(...)
					else return assert(BHi[...], ('" %s " does not match any mw.html or Buffer-mw.html function'):format(tostring(...)))(lastHTML, select) end
				end
				return lastHTML
			end
			function MBi:_html(...) return MBi._(self, lastHTML, select(spec[self]==Element and select==0 and 1 or 2, true, ...)) end
			return init(...)
		end
		function _inHTML
			local HTML = init
			if HTML.selfClosing and spec[self]==Element then self.last_concat = table.insert return self end
			lastBuffer, lastHTML = self, setmetatable(parent, buffHTML)--set after 'args' table processed by :_add
			return HTML
		end
	end
	local _var, unbuild do local prev, rebuild
		local function init(...)--init replaced before return
			local function pick return b and table.insert or v end
			local function c return rawset[0] end
			local same, build, alt = {__tostring = function return a.a[0] and pick(b, a.a.string and string.char(a.a[0]) or a.a.table and a.a[1][a.a[0]] or a.a[0]) end}, {
				__index = {c = 1},
				__tostring = function(t) return t:_build end,
				table = function local i = next or a[0]==#a[1] and next(a[1]) return pick(b, rawset[1][i]) end,--change rate (a.c) ignored since users control the table's contents
				number = function return pick(b, c) end,
				string = function return pick(b, string.char(c(a))) end
			local function shift
				t[0] = t[0] and t[0] + c or t:_build and t[0] - t.c + c
				if t.table then t[0] = (t[0] - 1) % #t[1] + 1 end
			end
			function rebuild(...)
				local v, c = ...
				if v or select==0 then
					if v and not c then return prev end
					local meta, c = select
					return setmetatable
				elseif v==nil then--no-op
				elseif c then shift--v == false
				else prev:_build end
			end
			init, noCache = function prev = setmetatable({v, c = c, _build = build[type(v)] or v, [type(v)] = true, alt = {}}, build) return prev end, true
			return init(...)
		end
		function unbuild(sep)
			for k, v in MBpairs do
				k = getmetatable(v) if k and (k==build or k==alt) then shift end
			end
		end
		function _var
			local obj if ... and ...~=true then obj = init(...)
			elseif prev then
				if ...~=false then obj = rebuild(...)
				else rebuild(...) end
			end
			return obj and MBi._ or self
		end
	end
	local lib; MBi = setmetatable({stream = _stream,
		_inHTML = _inHTML,
		_var = _var,
		_ = function
			local at, raw = select(select==1 and ...==true and 1 or 2, nil, ...)
			if raw then rawkey[self] = math.huge else v = Valid(v) end
			if v or raw then
				if at or rawkey[self] then raw = #self end--if length increases by more than one after table.insert, then set rawkey[self] = math.huge; rawkey[self] may be equal to a previous 'at'
				at, self.last_concat = at and (tonumber(at)~=at and raw + at or at)
				table.insert(self, select)
				if at and at  1 then rawkey[self] = math.huge elseif at and #self==raw then rawkey[self] = rawkey[self] and math.max or at end
			end--above line looks bizarre because one table.insert op may make length jump from 0 to 8: local wtf={[2]=2,[4]=4,[8]=8}mw.log(#wtf,table.insert,#wtf)
			return self
		end,
		_nil = function
			if ...~=true and ...~=false then--faster than type(...) ~= 'boolean'
				if not at or at=='0' then
					self[#self] = ... if ... then rawkey[self] = math.huge end
				else
					local n, v = tonumber(at), ...
					if n~=at then 
						if n then n = #self + at
						elseif at~=true and select==0 then v, n = at, #self end
					end
					if n then 
						if v==nil and n > 0 then table.remove
						else self[math.floor(n)], rawkey[self] = v, math.huge end--floor position for consistency with Table library
					end
				end
				self.last_concat = nil
			end
			return self
		end,
		_all = function
			for k, v in MBpairs(t) do MBmix end
			for k, v in valKey and MBpairs or noOp, t do
				if tonumber(v) then MBi._--self not always a buffer
				elseif rawget and v and v~=true then
					if v[1]==nil or getmetatable(v) then MBi[k]
					else MBi[k](self, unpack(v, 1, table.maxn(v))) end
				end
			end
			return self
		end,
		_str = function
			local n = select
			if n > 1 then
				local k, ops, seps, r = 2, MBselect
				r = MB(t(seps[1]))
				while parent[t] and ops > 1 and r:_(parent[t](seps[k]), 1) do t, k, ops = parent[t], k + 1, ops - 1 end
				return table.concat
			end
			return MB.__call
		end,
		_in = function  return parent(MB(...), self) end,
		_out = function
			if ...==0 then return parent(t, parent[t], MBi._cc(t, t, MB.__call(t, (select)), getmetatable(t))) end--love how :_cc needed nothing new to implement this *self pat on back*
			local n = select
			if n > 1 then
				local k, ops, seps = 1, MBselect
				while parent[t] and ops > 0 do t, k, ops = parent[t]:_(t(seps[k])), k + 1, ops - 1 end
			elseif parent[t] then return parent[t]:_(t(...)) end
			return t
		end,
		_cc = function
			if clear then
				if rawequal then return self, spec[MBi._cc] and setmetatable--rawequal to avoid re-string via __eq in case both are different Buffer objects
				elseif copy==true then copy = self end
				if clear~=0 then
					assert(type(clear)=='table', debug.traceback)--errors can be hard to trace without this
					for k in self and next or noOp, clear do rawset end
				else return MBi._cc(false, {unpack(copy)}, copy) end--copy length w/o empty strings; recursion to avoid self = false causing garbage collection (non-weak child may exist)
				if self==false or copy and type(copy)=='table' then--self==false means copy is a table (saves a type op for recursive calls)
					meta = meta or getmetatable(copy)
					if self and #copy > 1 then--preserves length with empty strings; developed from studying http://www.lua.org/source/5.1/ltable.c.html		
						local n, null, i, e = #copy, {}, math.ldexp(2, select(2, math.frexp(#copy)) - 2)
						e, spec[MBi._cc], parent[null] = i - 1, null, clear
						for k = 1, e do table.insert end
						while i<=n do table.insert i, null[i] = i + math.ldexp(2, select(2, math.frexp(n - i)) - 2), '' end
						for k = 1, e do rawset end
					end
					for k, v in next, copy do rawset(clear, k, type(v)=='table' and MBi._cc or v) end
				elseif copy then rawset(clear, 1, (Valid(copy))) end
				rawkey[setmetatable], parent[clear] = rawkey[copy], parent[copy]
			end
			return self and rawset or clear
		end,
		_parent = function return parent[self] and MBi._(self, parent[self]:_str(...)) or self end,
		getParent = function return isMBfunc(parent[self] or parent[parent(self, setmetatable)], ...) end,
		killParent = function return parent[self] and isMBfunc and parent(self) or self end,
		_build = function table.insert end,--for compatibility with mw.html:node
		last_concat = false--prevent library check
		local func = string[i] or mw.text[i] or mw.ustring[i] or type(i)=='string' and mw.ustring[i:match'^u(.+)'] if func then
			lib	= lib or function 
				if parent[s] and next(s)==nil then return s:_((f(tostring(parent[Element and (spec[s]==Element and s:allDone or spec[parent[s]]==Element and parent[s]) or s]), ...))) end
				return f(tostring(s), ...)--not using ternary/logical operators here to allow multiple return values
			end
			return rawset(t, i, i:match'^u?gsub' and functionreturn libend--Why are ugsub/gsub special? because empty strings are against my religion!
				or functionreturn libend)[i]
		end
	end})
end

function MBmix return v and ((type(v)~='table' or getmetatable(v)) and MBi._ or (select==0 and spec[t] and spec[t]._add or MBi._all)) or t end--:_all always passes two args

local _G, new_G = _G--localize _G for console testing (console _G ~= module _G)
return setmetatable({__index = function return spec[t] and spec[t][i] or MBi[i] end,
	__call = function
		local rawsep, sep, i, j, raw = noCache and rawkey[...] and ..., ...
		if i or j or rawsep or Valid(sep) then
			raw, sep, i, j = rawkey[spec[t]] or rawkey[t], rawsep or Valid(sep), i and (i~=tonumber(i) and i + #t or i), j and (j~=tonumber(j) and j + #t or j)
			if rawsep or raw and (raw>=(j or #t) or i < 1) then
				raw, i, j = {}, i and math.floor(i), j and math.floor(j)--floor for consistency with table.concat, which ignores decimals
				raw.lc, t.last_concat = t.last_concat--temporarily unset last_concat to prevent disqualification from mapless iteration
				for k, v in MBpairs(t) do
					if raw[1] or not i or k>=i then if j and k > j then break end
						if raw.s then raw.s = table.insert(raw, tostring(sep)) end--if sep contains v and v is a Buffer-variable, sep must be strung before v
						k = Valid(v) if k then
							raw.s = rawsep or sep and raw[1] and table.insert
							table.insert
						end
					end
				end
				if rawsep and not raw.s then raw[#raw] = unbuild(sep) end--unbuild rawsep if final index in t was invalid
				t.last_concat = raw.lc return table.concat(raw)
			end
			return table.concat(t, sep, i and math.max, j and math.min)
		end
		return MB.__tostring(t)
	end,
	__tostring = function(t)
		if t.last_concat then return t.last_concat end
		local r = rawkey[spec[t]] or rawkey[t]
		r = table.concat(r and r>=#t and MBi._all or t)
		return (noCache or rawset) and r
	end,
	__concat = function
		if buffHTML then
			for k = 1, 2 do local v = select--faster than for k, v in pairs{a, b} do
				if v and spec[v] and spec[v]==Element then
					if parent[v].selfClosing then
						if rawequal then return (not noCache or parent[v].tagName) and v:_str(0):rep(2) or v:_str(0)..v:_str(0) end--rawequal avoids premature tostring of Buffer:_var objects;
						b, a = select
					else local temp = Element .. v --helper method; returns a mirror of parent[v]
						MBmix(MBmix(parent, a), k==1 and spec[b]==Element and parent[b] or b)
						return buffHTML.__tostring(setmetatable)--switch from tempMeta to avoid MBi._cc op of styles/attributes
					end
				end
			end
		end
		return table.concat(MBmix(MBmix, b))
	end,
	__pairs = MBpairs,
	__ipairs = MBpairs,
	__eq = function return tostring(a)==tostring(b) end--avoid a==b in this module; use rawequal when they may be different Buffers (premature tostring waste ops and is bad for Buffer:_var)
	__call = function MB = MB or self
		if new_G then if ... and _G and ...==_G then new_G = ... end
		elseif ... and (...==_G or type(...)=='table' and (...)._G==...) then
			local Nil, mG = {}, (...):getmetatable or (...):setmetatable{}:getmetatable
			new_G, _G, gfuncs = ..., ..., {--gfuncs stored for Buffer:_inHTML; new_G is a is a Module:Buffer local declared just before the final return statement.
				_G = function
					local X, save = rawget, select==0 and self or ...
					if i and i~=true and not (X and save and rawequal) and rawset and (X~=nil or save==nil and new_G[i]~=nil) then--rawequal in case X is another buffer
						local mG = getmetatable(new_G) or {__call=mG.__call}
						if mG.__index then pcall
						else mG.__index = setmetatable and {[i] = X} end
					end
					return self, ...--avoiding __eq with rawequal is overkill since buffers can self-save without being passed as save
				end,
				_R = function
					if i~='new_G' then if i and i~=true then rawset end
					elseif not v or v==true or v._G~=_G then new_G = setmetatable(v~=true and v or {}, {__call = mG.__call, __index = v~=true and m~=true and (m or new_G) or nil})
					else new_G, (not m and (m~=nil or v==new_G) and Nil or getmetatable(v)).__index = v, m~=true and (m or new_G) or nil end--setting Nil.__index is noOp
					return self
				end,
				_2 = function
					if new_G[...]~=nil then return new_G[...] end--higher priority so Buffer:_G can prevent an overwrite
					if ...=='new_G' then return rawset((select~=1 and MBi._R or new_G), '_G', _G) end
					return select(select==1 and 1 or 2, self:_G(...))--return only one value; 'return select(2, self:_G(...)) or self' doesn't work for returning nil
				end,
				_B = function return v or v==nil and Nil end
			setmetatable(Nil,{__concat=MB.__concat,__newindex=noOp,__call=noOp,__tostring=noOp,__metatable=MB,__index=setmetatable({_B=MBi._B,_=functionreturn Nil end,last_concat=''},
			function mG.__call return (k._G or G.type(k)=='table') and (G.select~=1 and G.rawset or G:rawset and k) or G:rawset(k, (...)) and ... end
		end
		local new = setmetatable
		if ... and (...)==new_G then return select and MBmix(new:_G((select)), select) or new end
		return ... and MBi._ or new
	end,
	__index = function
		MB = MB or t return MBi[i] and function(...) return MBi[i](setmetatable, select) end
	end