Module:Section link

 -- This module implements {{section link}}.
 require('strict');

 localcheckType=require('libraryUtil').checkType

 localp={}

 localfunctionmakeSectionLink(page,section,display)
 display=displayorsection
 page=pageor''
 -- MediaWiki doesn't allow these in 'page', so only need to do for 'section'
 iftype(section)=='string'then
 section=string.gsub(section,"{","{")
 section=string.gsub(section,"}","}")
 end
 returnstring.format('[[%s#%s|%s]]',page,section,display)
 end

 localfunctionnormalizeTitle(title)
 title=mw.ustring.gsub(mw.ustring.gsub(title,"'",""),'"','')
 title=mw.ustring.gsub(title,"%b<>","")
 returnmw.title.new(title).prefixedText
 end

 functionp._main(page,sections,options,title)
 -- Validate input.
 checkType('_main',1,page,'string',true)
 checkType('_main',3,options,'table',true)
 ifsections==nilthen
 sections={}
 elseiftype(sections)=='string'then
 sections={sections}
 elseiftype(sections)~='table'then
 error(string.format(
 "type error in argument #2 to '_main' "..
 "(string, table or nil expected, got %s)",
 type(sections)
 ),2)
 end
 options=optionsor{}
 title=titleormw.title.getCurrentTitle()

 -- Deal with blank page names elegantly
 ifpageandnotpage:find('%S')then
 page=nil
 options.nopage=true
 end

 -- Make the link(s).
 localisShowingPage=notoptions.nopage
 if#sections<=1then
 locallinkPage=pageor''
 ifoptions.permalinkthen-- when oldid provided
 linkPage='Special:Permalink/'..options.permalink;-- make Special:Permalink/oldid wikilink
 end
 localsection=sections[1];-- sections[1] must have a value
 localdisplay='§&nbsp;'..section
 ifisShowingPagethen
 page=pageortitle.prefixedText
 ifoptions.displayandoptions.display~=''then
 ifnormalizeTitle(options.display)==normalizeTitle(page)then
 display=options.display..' '..display
 else
 error(string.format(
 'Display title "%s" was ignored since it is '..
 "not equivalent to the page's actual title",
 options.display
 ),0)
 end
 else
 display=page..' '..display
 end
 end
 returnmakeSectionLink(linkPage,section,display)
 else
 -- Multiple sections. First, make a list of the links to display.
 localret={}
 fori,sectioninipairs(sections)do
 ret[i]=makeSectionLink(page,section)
 end

 -- Assemble the list of links into a string with mw.text.listToText.
 -- We use the default separator for mw.text.listToText, but a custom
 -- conjunction. There is also a special case conjunction if we only
 -- have two links.
 localconjunction
 if#sections==2then
 conjunction='&#8203; and '
 else
 conjunction=', and '
 end
 ret=mw.text.listToText(ret,nil,conjunction)

 -- Add the intro text.
 localintro='§§&nbsp;'
 ifisShowingPagethen
 intro=(pageortitle.prefixedText)..' '..intro
 end
 ret=intro..ret

 returnret
 end
 end

 functionp.main(frame)
 localyesno=require('Module:Yesno')
 localargs=require('Module:Arguments').getArgs(frame,{
 wrappers='Template:Section link',
 valueFunc=function(key,value)
 value=value:match('^%s*(.-)%s*$')-- Trim whitespace
 -- Allow blank first parameters, as the wikitext template does this.
 ifvalue~=''orkey==1then
 returnvalue
 end
 end
 })

 fork,vinpairs(args)do-- replace underscores in the positional parameter values
 if'number'==type(k)then
 ifnotyesno(args['keep-underscores'])then-- unless |keep-underscores=yes
 args[k]=mw.uri.decode(v,'WIKI');-- percent-decode; replace underscores with space characters
 else
 args[k]=mw.uri.decode(v,'PATH');-- percent-decode; retain underscores
 end
 end
 end

 -- Sort the arguments.
 localpage
 localsections,options={},{}
 fork,vinpairs(args)do
 ifk==1then
 -- Doing this in the loop because of a bug in [[Module:Arguments]]
 -- when using pairs with deleted arguments.
 page=mw.text.decode(v,true)
 elseiftype(k)=='number'then
 sections[k]=v
 else
 options[k]=v
 end
 end

 options.nopage=yesno(options.nopage);-- make boolean

 -- Extract section from page, if present
 ifpagethen
 localp,s=page:match('^(.-)#(.*)$')
 ifpthenpage,sections[1]=p,send
 end

 -- Compress the sections array.
 localfunctioncompressArray(t)
 localnums,ret={},{}
 fornuminpairs(t)do
 nums[#nums+1]=num
 end
 table.sort(nums)
 fori,numinipairs(nums)do
 ret[i]=t[num]
 end
 returnret
 end
 sections=compressArray(sections)

 ifnotsections[1]then-- empty section parameter makes {{Section link}} meaningless
 return('<span style="color:#d33"><span style="font-family:monospace">{{[[Template:Section link|Section link]]}}</span>: required section parameter(s) missing</span>');-- emit error message and abandon
 end

 returnp._main(page,sections,options)
 end

 returnp