Module:Citation/CS1/Identifiers

 --[[--------------------------< F O R W A R D D E C L A R A T I O N S >--------------------------------------
 ]]

 localhas_accept_as_written,is_set,in_array,set_message,select_one,-- functions in Module:Citation/CS1/Utilities
 substitute,make_wikilink;

 localz;-- table of tables defined in Module:Citation/CS1/Utilities

 localcfg;-- table of configuration tables that are defined in Module:Citation/CS1/Configuration


 --[[--------------------------< P A G E S C O P E V A R I A B L E S >--------------------------------------

 declare variables here that have page-wide scope that are not brought in from other modules; that are created here and used here

 ]]

 localauto_link_urls={};-- holds identifier URLs for those identifiers that can auto-link |title=


 --============================<< H E L P E R F U N C T I O N S >>============================================

 --[[--------------------------< W I K I D A T A _ A R T I C L E _ N A M E _ G E T >----------------------------

 as an aid to internationalizing identifier-label wikilinks, gets identifier article names from Wikidata.

 returns w:<lang code>:<article title> when <q> has an <article title> for <lang code>; nil else. 'w:<lang code>'
 ensures that sister project (like wiktionary) will link to the <lang code>.wikipedia article.

 for identifiers that do not have <q>, returns nil

 for wikis that do not have mw.wikibase installed, returns nil

 ]]

 localfunctionwikidata_article_name_get(q)
 ifnotis_set(q)or(qandnotmw.wikibase)then-- when no q number or when a q number but mw.wikibase not installed on this wiki
 returnnil;-- abandon
 end

 localwd_article;
 localthis_wiki_code=cfg.this_wiki_code;-- Wikipedia subdomain; 'en' for en.wikipedia.org

 wd_article=mw.wikibase.getSitelink(q,this_wiki_code..'wiki');-- fetch article title from WD; nil when no title available at this wiki

 ifwd_articlethen
 wd_article=table.concat({'w:',this_wiki_code,':',wd_article});-- interwiki-style link without brackets if taken from WD; leading 'w:' required
 end

 returnwd_article;-- article title from WD; nil else
 end


 --[[--------------------------< L A B E L _ L I N K _ M A K E >------------------------------------------------

 common function to create a link for an identifier label from handler table or from Wikidata

 returns the first available of:
 	1. redirect from local wiki's handler table (if enabled)
 	2. Wikidata sitelink to the local language wikipedia article (if there is a Wikidata entry for this identifier in the local language)
 	3. link to wikipedia article specified in the local wiki's handler table

 ]]

 localfunctionlabel_link_make(handler)
 localwd_article;

 ifnot(cfg.use_identifier_redirectsandis_set(handler.redirect))then-- redirect has priority so if enabled and available don't fetch from Wikidata because expensive
 wd_article=wikidata_article_name_get(handler.q);-- if Wikidata has an article title for this wiki, get it;
 end

 return(cfg.use_identifier_redirectsandis_set(handler.redirect)andhandler.redirect)orwd_articleorhandler.link;
 end


 --[[--------------------------< E X T E R N A L _ L I N K _ I D >----------------------------------------------

 Formats a wiki-style external link

 ]]

 localfunctionexternal_link_id(options)
 localurl_string=options.id;
 localext_link;
 localthis_wiki_code=cfg.this_wiki_code;-- Wikipedia subdomain; 'en' for en.wikipedia.org
 localwd_article;-- article title from Wikidata

 ifoptions.encode==trueoroptions.encode==nilthen
 url_string=mw.uri.encode(url_string,'PATH');
 end

 ifoptions.auto_linkandis_set(options.access)then
 auto_link_urls[options.auto_link]=table.concat({options.prefix,url_string,options.suffix});
 end

 ext_link=mw.ustring.format('[%s%s%s %s]',options.prefix,url_string,options.suffixor"",mw.text.nowiki(options.id));
 ifis_set(options.access)then
 ext_link=substitute(cfg.presentation['ext-link-access-signal'],{cfg.presentation[options.access].class,cfg.presentation[options.access].title,ext_link});-- add the free-to-read / paywall lock
 end

 returntable.concat({
 make_wikilink(label_link_make(options),options.label),-- redirect, Wikidata link, or locally specified link (in that order)
 options.separatoror'&nbsp;',
 ext_link
 });
 end


 --[[--------------------------< I N T E R N A L _ L I N K _ I D >----------------------------------------------

 Formats a wiki-style internal link

 TODO: Does not currently need to support options.access, options.encode, auto-linking and COinS (as in external_link_id),
 but may be needed in the future for :m:Interwiki_map custom-prefixes like :arxiv:, :bibcode:, :DOI:, :hdl:, :ISSN:,
 :JSTOR:, :Openlibrary:, :PMID:, :RFC:.

 ]]

 localfunctioninternal_link_id(options)
 localid=mw.ustring.gsub(options.id,'%d',cfg.date_names.local_digits);-- translate 'local' digits to Western 0-9

 returntable.concat(
 {
 make_wikilink(label_link_make(options),options.label),-- wiki-link the identifier label
 options.separatoror'&nbsp;',-- add the separator
 make_wikilink(
 table.concat(
 {
 options.prefix,
 id,-- translated to Western digits
 options.suffixor''
 }),
 substitute(cfg.presentation['bdi'],{'',mw.text.nowiki(options.id)})-- bdi tags to prevent Latin script identifiers from being reversed at RTL language wikis
 );-- nowiki because MediaWiki still has magic links for ISBN and the like; TODO: is it really required?
 });
 end


 --[[--------------------------< I S _ E M B A R G O E D >------------------------------------------------------

 Determines if a PMC identifier's online version is embargoed. Compares the date in |pmc-embargo-date= against
 today's date. If embargo date is in the future, returns the content of |pmc-embargo-date=; otherwise, returns
 an empty string because the embargo has expired or because |pmc-embargo-date= was not set in this cite.

 ]]

 localfunctionis_embargoed(embargo)
 ifis_set(embargo)then
 locallang=mw.getContentLanguage();
 localgood1,embargo_date,todays_date;
 good1,embargo_date=pcall(lang.formatDate,lang,'U',embargo);
 todays_date=lang:formatDate('U');

 ifgood1then-- if embargo date is a good date
 iftonumber(embargo_date)>=tonumber(todays_date)then-- is embargo date is in the future?
 returnembargo;-- still embargoed
 else
 set_message('maint_pmc_embargo');-- embargo has expired; add main cat
 return'';-- unset because embargo has expired
 end
 end
 end
 return'';-- |pmc-embargo-date= not set return empty string
 end


 --[=[-------------------------< I S _ V A L I D _ R X I V _ D A T E >------------------------------------------

 for biorxiv, returns true if:
 	2019年12月11日T00:00Z <= biorxiv_date < today + 2 days
 for medrxiv, returns true if:
 	2020年01月01日T00:00Z <= medrxiv_date < today + 2 days

 The dated form of biorxiv identifier has a start date of 2019年12月11日. The Unix timestamp for that date is {{#time:U|2019年12月11日}} = 1576022400
 The medrxiv identifier has a start date of 2020年01月01日. The Unix timestamp for that date is {{#time:U|2020年01月01日}} = 1577836800

 <rxiv_date> is the date provided in those |biorxiv= parameter values that are dated and in |medrxiv= parameter values at time 00:00:00 UTC
 <today> is the current date at time 00:00:00 UTC plus 48 hours
 	if today's date is 2023年01月01日T00:00:00 then
 		adding 24 hours gives 2023年01月02日T00:00:00 – one second more than today
 		adding 24 hours gives 2023年01月03日T00:00:00 – one second more than tomorrow

 inputs:
 	<y>, <m>, <d> – year, month, day parts of the date from the birxiv or medrxiv identifier
 	<select> 'b' for biorxiv, 'm' for medrxiv; defaults to 'b'

 ]=]

 localfunctionis_valid_rxiv_date(y,m,d,select)
 if0==tonumber(m)and12<tonumber(m)then-- <m> must be a number 1–12
 returnfalse;
 end
 if0==tonumber(d)and31<tonumber(d)then-- <d> must be a number 1–31; TODO: account for month length and leap yer?
 returnfalse;
 end

 localrxiv_date=table.concat({y,m,d},'-');-- make ymd date string
 localgood1,good2;
 localrxiv_ts,tomorrow_ts;-- to hold Unix timestamps representing the dates
 locallang_object=mw.getContentLanguage();

 good1,rxiv_ts=pcall(lang_object.formatDate,lang_object,'U',rxiv_date);-- convert rxiv_date value to Unix timestamp 
 good2,tomorrow_ts=pcall(lang_object.formatDate,lang_object,'U','today + 2 days');-- today midnight + 2 days is one second more than all day tomorrow

 ifgood1andgood2then-- lang.formatDate() returns a timestamp in the local script which tonumber() may not understand
 rxiv_ts=tonumber(rxiv_ts)orlang_object:parseFormattedNumber(rxiv_ts);-- convert to numbers for the comparison;
 tomorrow_ts=tonumber(tomorrow_ts)orlang_object:parseFormattedNumber(tomorrow_ts);
 else
 returnfalse;-- one or both failed to convert to Unix timestamp
 end

 locallimit_ts=((selectand('m'==select))and1577836800)or1576022400;-- choose the appropriate limit timesatmp

 return((limit_ts<=rxiv_ts)and(rxiv_ts<tomorrow_ts))-- limit_ts <= rxiv_date < tomorrow's date
 end


 --[[--------------------------< IS _ V A L I D _ I S X N >-----------------------------------------------------

 ISBN-10 and ISSN validator code calculates checksum across all ISBN/ISSN digits including the check digit.
 ISBN-13 is checked in isbn().

 If the number is valid the result will be 0. Before calling this function, ISBN/ISSN must be checked for length
 and stripped of dashes, spaces and other non-ISxN characters.

 ]]

 localfunctionis_valid_isxn(isxn_str,len)
 localtemp=0;
 isxn_str={isxn_str:byte(1,len)};-- make a table of byte values '0' → 0x30 .. '9' → 0x39, 'X' → 0x58
 len=len+1;-- adjust to be a loop counter
 fori,vinipairs(isxn_str)do-- loop through all of the bytes and calculate the checksum
 ifv==string.byte("X")then-- if checkdigit is X (compares the byte value of 'X' which is 0x58)
 temp=temp+10*(len-i);-- it represents 10 decimal
 else
 temp=temp+tonumber(string.char(v))*(len-i);
 end
 end
 returntemp%11==0;-- returns true if calculation result is zero
 end


 --[[--------------------------< IS _ V A L I D _ I S X N _ 1 3 >-----------------------------------------------

 ISBN-13 and ISMN validator code calculates checksum across all 13 ISBN/ISMN digits including the check digit.
 If the number is valid, the result will be 0. Before calling this function, ISBN-13/ISMN must be checked for length
 and stripped of dashes, spaces and other non-ISxN-13 characters.

 ]]

 localfunctionis_valid_isxn_13(isxn_str)
 localtemp=0;

 isxn_str={isxn_str:byte(1,13)};-- make a table of byte values '0' → 0x30 .. '9' → 0x39
 fori,vinipairs(isxn_str)do
 temp=temp+(3-2*(i%2))*tonumber(string.char(v));-- multiply odd index digits by 1, even index digits by 3 and sum; includes check digit
 end
 returntemp%10==0;-- sum modulo 10 is zero when ISBN-13/ISMN is correct
 end


 --[[--------------------------< N O R M A L I Z E _ L C C N >--------------------------------------------------

 LCCN normalization (https://www.loc.gov/marc/lccn-namespace.html#normalization)
 1. Remove all blanks.
 2. If there is a forward slash (/) in the string, remove it, and remove all characters to the right of the forward slash.
 3. If there is a hyphen in the string:
 	a. Remove it.
 	b. Inspect the substring following (to the right of) the (removed) hyphen. Then (and assuming that steps 1 and 2 have been carried out):
 		1. All these characters should be digits, and there should be six or less. (not done in this function)
 		2. If the length of the substring is less than 6, left-fill the substring with zeroes until the length is six.

 Returns a normalized LCCN for lccn() to validate. There is no error checking (step 3.b.1) performed in this function.

 ]]

 localfunctionnormalize_lccn(lccn)
 lccn=lccn:gsub("%s","");-- 1. strip whitespace

 ifnil~=string.find(lccn,'/')then
 lccn=lccn:match("(.-)/");-- 2. remove forward slash and all character to the right of it
 end

 localprefix
 localsuffix
 prefix,suffix=lccn:match("(.+)%-(.+)");-- 3.a remove hyphen by splitting the string into prefix and suffix

 ifnil~=suffixthen-- if there was a hyphen
 suffix=string.rep("0",6-string.len(suffix))..suffix;-- 3.b.2 left fill the suffix with 0s if suffix length less than 6
 lccn=prefix..suffix;-- reassemble the LCCN
 end

 returnlccn;
 end


 --============================<< I D E N T I F I E R F U N C T I O N S >>====================================

 --[[--------------------------< A R X I V >--------------------------------------------------------------------

 See: https://arxiv.org/help/arxiv_identifier

 format and error check arXiv identifier. There are three valid forms of the identifier:
 the first form, valid only between date codes 9107 and 0703, is:
 	arXiv:<archive>.<class>/<date code><number><version>
 where:
 	<archive> is a string of alpha characters - may be hyphenated; no other punctuation
 	<class> is a string of alpha characters - may be hyphenated; no other punctuation; not the same as |class= parameter which is not supported in this form
 	<date code> is four digits in the form YYMM where YY is the last two digits of the four-digit year and MM is the month number January = 01
 		first digit of YY for this form can only 9 and 0
 	<number> is a three-digit number
 	<version> is a 1 or more digit number preceded with a lowercase v; no spaces (undocumented)

 the second form, valid from April 2007 through December 2014 is:
 	arXiv:<date code>.<number><version>
 where:
 	<date code> is four digits in the form YYMM where YY is the last two digits of the four-digit year and MM is the month number January = 01
 	<number> is a four-digit number
 	<version> is a 1 or more digit number preceded with a lowercase v; no spaces

 the third form, valid from January 2015 is:
 	arXiv:<date code>.<number><version>
 where:
 	<date code> and <version> are as defined for 0704-1412
 	<number> is a five-digit number

 ]]

 localfunctionarxiv(options)
 localid=options.id;
 localclass=options.Class;-- TODO: lowercase?
 localhandler=options.handler;
 localyear,month,version;
 localerr_msg=false;-- assume no error message
 localtext;-- output text

 ifid:match("^%a[%a%.%-]+/[90]%d[01]%d%d%d%d$")orid:match("^%a[%a%.%-]+/[90]%d[01]%d%d%d%dv%d+$")then-- test for the 9107-0703 format with or without version
 year,month=id:match("^%a[%a%.%-]+/([90]%d)([01]%d)%d%d%d[v%d]*$");
 year=tonumber(year);
 month=tonumber(month);
 if((not(90<yearor8>year))or(1>monthor12<month))or-- if invalid year or invalid month
 ((91==yearand7>month)or(7==yearand3<month))then-- if years ok, are starting and ending months ok?
 err_msg=true;-- flag for error message
 end

 elseifid:match("^%d%d[01]%d%.%d%d%d%d$")orid:match("^%d%d[01]%d%.%d%d%d%dv%d+$")then-- test for the 0704-1412 with or without version
 year,month=id:match("^(%d%d)([01]%d)%.%d%d%d%d[v%d]*$");
 year=tonumber(year);
 month=tonumber(month);
 if((7>year)or(14<year)or(1>monthor12<month))or-- is year invalid or is month invalid? (doesn't test for future years)
 ((7==year)and(4>month))then-- when year is 07, is month invalid (before April)?
 err_msg=true;-- flag for error message
 end

 elseifid:match("^%d%d[01]%d%.%d%d%d%d%d$")orid:match("^%d%d[01]%d%.%d%d%d%d%dv%d+$")then-- test for the 1501- format with or without version
 year,month=id:match("^(%d%d)([01]%d)%.%d%d%d%d%d[v%d]*$");
 year=tonumber(year);
 month=tonumber(month);
 if((15>year)or(1>monthor12<month))then-- is year invalid or is month invalid? (doesn't test for future years)
 err_msg=true;-- flag for error message
 end

 else
 err_msg=true;-- not a recognized format; flag for error message
 end

 iferr_msgthen
 options.coins_list_t['ARXIV']=nil;-- when error, unset so not included in COinS
 end

 localerr_msg_t={};
 iferr_msgthen
 set_message('err_bad_arxiv');
 end

 text=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=handler.access});

 ifis_set(class)then
 ifid:match('^%d+')then
 text=table.concat({text,' [[https://arxiv.org/archive/',class,' ',class,']]'});-- external link within square brackets, not wikilink
 else
 set_message('err_class_ignored');
 end
 else-- class not set
 ifid:match('^%d+')andoptions.CitationClass=='arxiv'then-- new (post 2007) format; {{cite arxiv}} only
 set_message('maint_missing_class');-- add maint cat
 end
 end

 returntext;
 end


 --[[--------------------------< B I B C O D E >--------------------------------------------------------------------

 Validates (sort of) and formats a bibcode ID.

 Format for bibcodes is specified here: https://adsabs.harvard.edu/abs_doc/help_pages/data.html#bibcodes

 But, this: 2015arXiv151206696F is apparently valid so apparently, the only things that really matter are length, 19 characters
 and first four digits must be a year. This function makes these tests:
 	length must be 19 characters
 	characters in position
 		1–4 must be digits and must represent a year in the range of 1000 – next year
 		5 must be a letter
 		6–8 must be letter, digit, ampersand, or dot (ampersand cannot directly precede a dot; &. )
 		9–18 must be letter, digit, or dot
 		19 must be a letter or dot

 ]]

 localfunctionbibcode(options)
 localid=options.id;
 localaccess=options.access;
 localhandler=options.handler;
 localignore_invalid=options.accept;
 localerr_type;
 localerr_msg='';
 localyear;

 localtext=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,
 access=access});

 if19~=id:len()then
 err_type=cfg.err_msg_supl.length;
 else
 year=id:match("^(%d%d%d%d)[%a][%w&%.][%w&%.][%w&%.][%w.]+[%a%.]$");
 ifnotyearthen-- if nil then no pattern match
 err_type=cfg.err_msg_supl.value;-- so value error
 else
 localnext_year=tonumber(os.date('%Y'))+1;-- get the current year as a number and add one for next year
 year=tonumber(year);-- convert year portion of bibcode to a number
 if(1000>year)or(year>next_year)then
 err_type=cfg.err_msg_supl.year;-- year out of bounds
 end
 ifid:find('&%.')then
 err_type=cfg.err_msg_supl.journal;-- journal abbreviation must not have '&.' (if it does it's missing a letter)
 end
 ifid:match('.........%.tmp%.')then-- temporary bibcodes when positions 10–14 are '.tmp.'
 set_message('maint_bibcode');
 end
 end
 end

 ifis_set(err_type)andnotignore_invalidthen-- if there was an error detected and accept-as-written markup not used
 set_message('err_bad_bibcode',{err_type});
 options.coins_list_t['BIBCODE']=nil;-- when error, unset so not included in COinS
 end

 returntext;
 end


 --[[--------------------------< B I O R X I V >-----------------------------------------------------------------

 Format bioRxiv ID and do simple error checking. Before 2019年12月11日, biorXiv IDs were 10.1101/ followed by exactly
 6 digits. After 2019年12月11日, biorXiv IDs retained the six-digit identifier but prefixed that with a yyyy.mm.dd. 
 date and suffixed with an optional version identifier.

 The bioRxiv ID is the string of characters:
 	https://doi.org/10.1101/078733 -> 10.1101/078733
 or a date followed by a six-digit number followed by an optional version indicator 'v' and one or more digits:
 	https://www.biorxiv.org/content/10.1101/2019.12.11.123456v2 -> 10.1101/2019.12.11.123456v2

 see https://www.biorxiv.org/about-biorxiv

 ]]

 localfunctionbiorxiv(options)
 localid=options.id;
 localhandler=options.handler;
 localerr_msg=true;-- flag; assume that there will be an error

 localpatterns={
 '^10%.1101/%d%d%d%d%d%d$',-- simple 6-digit identifier (before 2019年12月11日)
 '^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%dv%d+$',-- y.m.d. date + 6-digit identifier + version (after 2019年12月11日)
 '^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%d$',-- y.m.d. date + 6-digit identifier (after 2019年12月11日)
 }

 for_,patterninipairs(patterns)do-- spin through the patterns looking for a match
 ifid:match(pattern)then
 localy,m,d=id:match(pattern);-- found a match, attempt to get year, month and date from the identifier

 ifmthen-- m is nil when id is the six-digit form
 ifnotis_valid_rxiv_date(y,m,d,'b')then-- validate the encoded date; 'b' for biorxiv limit
 break;-- date fail; break out early so we don't unset the error message
 end
 end
 err_msg=nil;-- we found a match so unset the error message
 break;-- and done
 end
 end-- err_cat remains set here when no match

 iferr_msgthen
 options.coins_list_t['BIORXIV']=nil;-- when error, unset so not included in COinS
 set_message('err_bad_biorxiv');-- and set the error message
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,
 encode=handler.encode,access=handler.access});
 end


 --[[--------------------------< C I T E S E E R X >------------------------------------------------------------

 CiteSeerX use their own notion of "doi" (not to be confused with the identifiers resolved via doi.org).

 The description of the structure of this identifier can be found at Help_talk:Citation_Style_1/Archive_26#CiteSeerX_id_structure

 ]]

 localfunctionciteseerx(options)
 localid=options.id;
 localhandler=options.handler;
 localmatched;

 localtext=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,
 access=handler.access});

 matched=id:match("^10%.1%.1%.[1-9]%d?%d?%d?%.[1-9]%d?%d?%d?$");
 ifnotmatchedthen
 set_message('err_bad_citeseerx');
 options.coins_list_t['CITESEERX']=nil;-- when error, unset so not included in COinS
 end

 returntext;
 end


 --[[--------------------------< D O I >------------------------------------------------------------------------

 Formats a DOI and checks for DOI errors.

 DOI names contain two parts: prefix and suffix separated by a forward slash.
 	Prefix: directory indicator '10.' followed by a registrant code
 	Suffix: character string of any length chosen by the registrant

 This function checks a DOI name for: prefix/suffix. If the DOI name contains spaces or endashes, or, if it ends
 with a period or a comma, this function will emit a bad_doi error message.

 DOI names are case-insensitive and can incorporate any printable Unicode characters so the test for spaces, endash,
 and terminal punctuation may not be technically correct but it appears, that in practice these characters are rarely
 if ever used in DOI names.

 https://www.doi.org/doi_handbook/2_Numbering.html				-- 2.2 Syntax of a DOI name
 https://www.doi.org/doi_handbook/2_Numbering.html#2.2.2			-- 2.2.2 DOI prefix

 ]]

 localfunctiondoi(options)
 localid=options.id;
 localinactive=options.DoiBroken
 localaccess=options.access;
 localignore_invalid=options.accept;
 localhandler=options.handler;
 localerr_flag;

 localfunctionis_extended_free(registrant,suffix)-- local function to check those few registrants that are mixed; identifiable by the doi suffix <incipit>
 ifcfg.extended_registrants_t[registrant]then-- if this registrant has known free-to-read extentions
 for_,incipitinipairs(cfg.extended_registrants_t[registrant])do-- loop through the registrant's incipits
 ifmw.ustring.find(suffix,'^'..incipit)then-- if found
 returntrue;
 end
 end
 end
 end

 localtext;
 ifis_set(inactive)then
 localinactive_year=inactive:match("%d%d%d%d");-- try to get the year portion from the inactive date
 localinactive_month,good;

 ifis_set(inactive_year)then
 if4<inactive:len()then-- inactive date has more than just a year (could be anything)
 locallang_obj=mw.getContentLanguage();-- get a language object for this wiki
 good,inactive_month=pcall(lang_obj.formatDate,lang_obj,'F',inactive);-- try to get the month name from the inactive date
 ifnotgoodthen
 inactive_month=nil;-- something went wrong so make sure this is unset
 end
 end
 end-- otherwise, |doi-broken-date= has something but it isn't a date

 ifis_set(inactive_year)andis_set(inactive_month)then
 set_message('maint_doi_inactive_dated',{inactive_year,inactive_month,' '});
 elseifis_set(inactive_year)then
 set_message('maint_doi_inactive_dated',{inactive_year,'',''});
 else
 set_message('maint_doi_inactive');
 end
 inactive=" ("..cfg.messages['inactive']..' '..inactive..')';
 end

 localsuffix;
 localregistrant,suffix=mw.ustring.match(id,'^10%.([^/]+)/([^%s–]-[^%.,])$');-- registrant and suffix set when DOI has the proper basic form

 localregistrant_err_patterns={-- these patterns are for code ranges that are not supported 
 '^[^1-3]%d%d%d%d%.%d+$',-- 5 digits with subcode (0xxxx, 40000+); accepts: 10000–39999
 '^[^1-7]%d%d%d%d$',-- 5 digits without subcode (0xxxx, 60000+); accepts: 10000–69999
 '^[^1-9]%d%d%d%.%d+$',-- 4 digits with subcode (0xxx); accepts: 1000–9999
 '^[^1-9]%d%d%d$',-- 4 digits without subcode (0xxx); accepts: 1000–9999
 '^%d%d%d%d%d%d+',-- 6 or more digits
 '^%d%d?%d?$',-- less than 4 digits without subcode (3 digits with subcode is legitimate)
 '^%d%d?%.[%d%.]+',-- 1 or 2 digits with subcode
 '^5555$',-- test registrant will never resolve
 '[^%d%.]',-- any character that isn't a digit or a dot
 }

 ifnotignore_invalidthen
 ifregistrantthen-- when DOI has proper form
 fori,patterninipairs(registrant_err_patterns)do-- spin through error patterns
 ifregistrant:match(pattern)then-- to validate registrant codes
 err_flag=set_message('err_bad_doi');-- when found, mark this DOI as bad
 break;-- and done
 end
 end
 else
 err_flag=set_message('err_bad_doi');-- invalid directory or malformed
 end
 else
 set_message('maint_doi_ignore');
 end

 iferr_flagthen
 options.coins_list_t['DOI']=nil;-- when error, unset so not included in COinS
 else
 ifnotaccessand(cfg.known_free_doi_registrants_t[registrant]oris_extended_free(registrant,suffix))then-- |doi-access=free not set and <registrant> is known to be free
 set_message('maint_doi_unflagged_free');-- set a maint cat
 end
 end

 text=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=access,
 auto_link=not(err_flagoris_set(inactive)orignore_invalid)and'doi'ornil-- do not auto-link when |doi-broken-date= has a value or when there is a DOI error or (to play it safe, after all, auto-linking is not essential) when invalid DOIs are ignored
 })..(inactiveor'');

 returntext;
 end


 --[[--------------------------< H D L >------------------------------------------------------------------------

 Formats an HDL with minor error checking.

 HDL names contain two parts: prefix and suffix separated by a forward slash.
 	Prefix: character string using any character in the UCS-2 character set except '/'
 	Suffix: character string of any length using any character in the UCS-2 character set chosen by the registrant

 This function checks a HDL name for: prefix/suffix. If the HDL name contains spaces, endashes, or, if it ends
 with a period or a comma, this function will emit a bad_hdl error message.

 HDL names are case-insensitive and can incorporate any printable Unicode characters so the test for endashes and
 terminal punctuation may not be technically correct but it appears, that in practice these characters are rarely
 if ever used in HDLs.

 Query string parameters are named here: https://www.handle.net/proxy_servlet.html. query strings are not displayed
 but since '?' is an allowed character in an HDL, '?' followed by one of the query parameters is the only way we
 have to detect the query string so that it isn't URL-encoded with the rest of the identifier.

 ]]

 localfunctionhdl(options)
 localid=options.id;
 localaccess=options.access;
 localhandler=options.handler;
 localquery_params={-- list of known query parameters from https://www.handle.net/proxy_servlet.html
 'noredirect',
 'ignore_aliases',
 'auth',
 'cert',
 'index',
 'type',
 'urlappend',
 'locatt',
 'action',
 }

 localhdl,suffix,param=id:match('(.-)(%?(%a+).+)$');-- look for query string
 localfound;

 ifhdlthen-- when there are query strings, this is the handle identifier portion
 for_,qinipairs(query_params)do-- spin through the list of query parameters
 ifparam:match('^'..q)then-- if the query string begins with one of the parameters
 found=true;-- announce a find
 break;-- and stop looking
 end
 end
 end

 iffoundthen
 id=hdl;-- found so replace id with the handle portion; this will be URL-encoded, suffix will not
 else
 suffix='';-- make sure suffix is empty string for concatenation else
 end

 localtext=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,suffix=suffix,separator=handler.separator,encode=handler.encode,access=access})

 ifnil==id:match("^[^%s–]-/[^%s–]-[^%.,]$")then-- HDL must contain a forward slash, must not contain spaces, endashes, and must not end with period or comma
 set_message('err_bad_hdl');
 options.coins_list_t['HDL']=nil;-- when error, unset so not included in COinS
 end

 returntext;
 end


 --[[--------------------------< I S B N >----------------------------------------------------------------------

 Determines whether an ISBN string is valid

 ]]

 localfunctionisbn(options_t)
 localisbn_str=options_t.id;
 localignore_invalid=options_t.accept;
 localhandler=options_t.handler;
 localyear=options_t.Year;-- when set, valid anchor_year; may have a disambiguator which must be removed

 localfunctionreturn_result(check,err_type)-- local function to handle the various returns
 localISBN=internal_link_id({link=handler.link,label=handler.label,redirect=handler.redirect,
 prefix=handler.prefix,id=isbn_str,separator=handler.separator});
 ifignore_invalidthen-- if ignoring ISBN errors
 set_message('maint_isbn_ignore');-- add a maint category even when there is no error
 else-- here when not ignoring
 ifnotcheckthen-- and there is an error
 options_t.coins_list_t['ISBN']=nil;-- when error, unset so not included in COinS
 set_message('err_bad_isbn',err_type);-- set an error message
 returnISBN;-- return id text
 end
 end
 returnISBN;-- return id text
 end

 ifyearandnotignore_invalidthen-- 
 year=year:match('%d%d%d%d?');-- strip disambiguator if present
 ifyearand(1965>tonumber(year))then-- <year> will be nil here when |year=n.d. or |year=nd
 set_message('err_invalid_isbn_date');-- set an error message
 returninternal_link_id({link=handler.link,label=handler.label,redirect=handler.redirect,
 prefix=handler.prefix,id=isbn_str,separator=handler.separator});
 end
 end

 ifnil~=isbn_str:match('[^%s-0-9X]')then
 returnreturn_result(false,cfg.err_msg_supl.char);-- fail if isbn_str contains anything but digits, hyphens, or the uppercase X
 end

 localid=isbn_str:gsub('[%s-]','');-- remove hyphens and whitespace

 locallen=id:len();

 iflen~=10andlen~=13then
 returnreturn_result(false,cfg.err_msg_supl.length);-- fail if incorrect length
 end

 iflen==10then
 ifid:match('^%d*X?$')==nilthen-- fail if isbn_str has 'X' anywhere but last position
 returnreturn_result(false,cfg.err_msg_supl.form);
 end
 ifnotis_valid_isxn(id,10)then-- test isbn-10 for numerical validity
 returnreturn_result(false,cfg.err_msg_supl.check);-- fail if isbn-10 is not numerically valid
 end
 ifid:find('^63[01]')then-- 630xxxxxxx and 631xxxxxxx are (apparently) not valid isbn group ids but are used by amazon as numeric identifiers (asin)
 returnreturn_result(false,cfg.err_msg_supl.group);-- fail if isbn-10 begins with 630/1
 end
 returnreturn_result(true,cfg.err_msg_supl.check);-- pass if isbn-10 is numerically valid
 else
 ifid:match('^%d+$')==nilthen
 returnreturn_result(false,cfg.err_msg_supl.char);-- fail if ISBN-13 is not all digits
 end
 ifid:match('^97[89]%d*$')==nilthen
 returnreturn_result(false,cfg.err_msg_supl.prefix);-- fail when ISBN-13 does not begin with 978 or 979
 end
 ifid:match('^9790')then
 returnreturn_result(false,cfg.err_msg_supl.group);-- group identifier '0' is reserved to ISMN
 end
 returnreturn_result(is_valid_isxn_13(id),cfg.err_msg_supl.check);
 end
 end


 --[[--------------------------< A S I N >----------------------------------------------------------------------

 Formats a link to Amazon. Do simple error checking: ASIN must be mix of 10 numeric or uppercase alpha
 characters. If a mix, first character must be uppercase alpha; if all numeric, ASINs must be 10-digit
 ISBN. If 10-digit ISBN, add a maintenance category so a bot or AWB script can replace |asin= with |isbn=.
 Error message if not 10 characters, if not ISBN-10, if mixed and first character is a digit.

 |asin=630....... and |asin=631....... are (apparently) not a legitimate ISBN though it checksums as one; these
 do not cause this function to emit the maint_asin message

 This function is positioned here because it calls isbn()

 ]]

 localfunctionasin(options)
 localid=options.id;
 localdomain=options.ASINTLD;

 localerr_flag;

 ifnotid:match("^[%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u][%d%u]$")then
 err_flag=set_message('err_bad_asin');-- ASIN is not a mix of 10 uppercase alpha and numeric characters
 else
 ifid:match("^%d%d%d%d%d%d%d%d%d[%dX]$")then-- if 10-digit numeric (or 9 digits with terminal X)
 ifis_valid_isxn(id,10)then-- see if ASIN value is or validates as ISBN-10
 ifnotid:find('^63[01]')then-- 630xxxxxxx and 631xxxxxxx are (apparently) not a valid isbn prefixes but are used by amazon as a numeric identifier
 err_flag=set_message('err_bad_asin');-- ASIN has ISBN-10 form but begins with something other than 630/1 so probably an isbn 
 end
 elseifnotis_set(err_flag)then
 err_flag=set_message('err_bad_asin');-- ASIN is not ISBN-10
 end
 elseifnotid:match("^%u[%d%u]+$")then
 err_flag=set_message('err_bad_asin');-- asin doesn't begin with uppercase alpha
 end
 end
 if(notis_set(domain))orin_array(domain,{'us'})then-- default: United States
 domain="com";
 elseifin_array(domain,{'jp','uk'})then-- Japan, United Kingdom
 domain="co."..domain;
 elseifin_array(domain,{'z.cn'})then-- China
 domain="cn";
 elseifin_array(domain,{'au','br','mx','sg','tr'})then-- Australia, Brazil, Mexico, Singapore, Turkey
 domain="com."..domain;
 elseifnotin_array(domain,{'ae','ca','cn','de','es','fr','in','it','nl','pl','sa','se','co.jp','co.uk','com','com.au','com.br','com.mx','com.sg','com.tr'})then-- Arabic Emirates, Canada, China, Germany, Spain, France, Indonesia, Italy, Netherlands, Poland, Saudi Arabia, Sweden (as of 2021-03 Austria (.at), Liechtenstein (.li) and Switzerland (.ch) still redirect to the German site (.de) with special settings, so don't maintain local ASINs for them)
 err_flag=set_message('err_bad_asin_tld');-- unsupported asin-tld value
 end
 localhandler=options.handler;

 ifnotis_set(err_flag)then
 options.coins_list_t['ASIN']=handler.prefix..domain.."/dp/"..id;-- asin for coins
 else
 options.coins_list_t['ASIN']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix..domain.."/dp/",
 id=id,encode=handler.encode,separator=handler.separator})
 end


 --[[--------------------------< I S M N >----------------------------------------------------------------------

 Determines whether an ISMN string is valid. Similar to ISBN-13, ISMN is 13 digits beginning 979-0-... and uses the
 same check digit calculations. See https://www.ismn-international.org/download/Web_ISMN_Users_Manual_2008-6.pdf
 section 2, pages 9–12.

 ismn value not made part of COinS metadata because we don't have a url or isn't a COinS-defined identifier (rft.xxx)
 or an identifier registered at info-uri.info (info:)

 ]]

 localfunctionismn(options)
 localid=options.id;
 localhandler=options.handler;
 localtext;
 localvalid_ismn=true;
 localid_copy;

 id_copy=id;-- save a copy because this testing is destructive
 id=id:gsub('[%s-]','');-- remove hyphens and white space

 if13~=id:len()orid:match("^9790%d*$")==nilthen-- ISMN must be 13 digits and begin with 9790
 valid_ismn=false;
 else
 valid_ismn=is_valid_isxn_13(id);-- validate ISMN
 end

 --	text = internal_link_id ({link = handler.link, label = handler.label, q = handler.q, redirect = handler.redirect,		-- use this (or external version) when there is some place to link to
 --		prefix = handler.prefix, id = id_copy, separator = handler.separator, encode = handler.encode})

 text=table.concat(-- because no place to link to yet
 {
 make_wikilink(label_link_make(handler),handler.label),
 handler.separator,
 id_copy
 });

 iffalse==valid_ismnthen
 options.coins_list_t['ISMN']=nil;-- when error, unset so not included in COinS; not really necessary here because ismn not made part of COinS
 set_message('err_bad_ismn');-- create an error message if the ISMN is invalid
 end

 returntext;
 end


 --[[--------------------------< I S S N >----------------------------------------------------------------------

 Validate and format an ISSN. This code fixes the case where an editor has included an ISSN in the citation but
 has separated the two groups of four digits with a space. When that condition occurred, the resulting link looked
 like this:

 	|issn=0819 4327 gives: [https://www.worldcat.org/issn/0819 4327 0819 4327]	-- can't have spaces in an external link

 This code now prevents that by inserting a hyphen at the ISSN midpoint. It also validates the ISSN for length
 and makes sure that the checkdigit agrees with the calculated value. Incorrect length (8 digits), characters
 other than 0-9 and X, or checkdigit / calculated value mismatch will all cause a check ISSN error message. The
 ISSN is always displayed with a hyphen, even if the ISSN was given as a single group of 8 digits.

 ]]

 localfunctionissn(options)
 localid=options.id;
 localhandler=options.handler;
 localignore_invalid=options.accept;

 localissn_copy=id;-- save a copy of unadulterated ISSN; use this version for display if ISSN does not validate
 localtext;
 localvalid_issn=true;

 id=id:gsub('[%s-]','');-- remove hyphens and whitespace

 if8~=id:len()ornil==id:match("^%d*X?$")then-- validate the ISSN: 8 digits long, containing only 0-9 or X in the last position
 valid_issn=false;-- wrong length or improper character
 else
 valid_issn=is_valid_isxn(id,8);-- validate ISSN
 end

 iftrue==valid_issnthen
 id=string.sub(id,1,4).."-"..string.sub(id,5);-- if valid, display correctly formatted version
 else
 id=issn_copy;-- if not valid, show the invalid ISSN with error message
 end

 text=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode})

 ifignore_invalidthen
 set_message('maint_issn_ignore');
 else
 iffalse==valid_issnthen
 options.coins_list_t['ISSN']=nil;-- when error, unset so not included in COinS
 set_message('err_bad_issn',(options.hkey=='EISSN')and'e'or'');-- create an error message if the ISSN is invalid
 end
 end

 returntext;
 end


 --[[--------------------------< J F M >-----------------------------------------------------------------------

 A numerical identifier in the form nn.nnnn.nn

 ]]

 localfunctionjfm(options)
 localid=options.id;
 localhandler=options.handler;
 localid_num;

 id_num=id:match('^[Jj][Ff][Mm](.*)$');-- identifier with jfm prefix; extract identifier

 ifis_set(id_num)then
 set_message('maint_jfm_format');
 else-- plain number without JFM prefix
 id_num=id;-- if here id does not have prefix
 end

 ifid_numandid_num:match('^%d%d%.%d%d%d%d%.%d%d$')then
 id=id_num;-- jfm matches pattern
 else
 set_message('err_bad_jfm');-- set an error message
 options.coins_list_t['JFM']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode});
 end


 --[[--------------------------< J S T O R >--------------------------------------------------------------------

 Format a JSTOR with some error checking

 ]]

 localfunctionjstor(options)
 localid=options.id;
 localaccess=options.access;
 localhandler=options.handler;

 ifid:find('[Jj][Ss][Tt][Oo][Rr]')orid:find('^https?://')orid:find('%s')then
 set_message('err_bad_jstor');-- set an error message
 options.coins_list_t['JSTOR']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=access});
 end


 --[[--------------------------< L C C N >----------------------------------------------------------------------

 Format LCCN link and do simple error checking. LCCN is a character string 8-12 characters long. The length of
 the LCCN dictates the character type of the first 1-3 characters; the rightmost eight are always digits.
 https://oclc-research.github.io/infoURI-Frozen/info-uri.info/info:lccn/reg.html

 length = 8 then all digits
 length = 9 then lccn[1] is lowercase alpha
 length = 10 then lccn[1] and lccn[2] are both lowercase alpha or both digits
 length = 11 then lccn[1] is lower case alpha, lccn[2] and lccn[3] are both lowercase alpha or both digits
 length = 12 then lccn[1] and lccn[2] are both lowercase alpha

 ]]

 localfunctionlccn(options)
 locallccn=options.id;
 localhandler=options.handler;
 localerr_flag;-- presume that LCCN is valid
 localid=lccn;-- local copy of the LCCN

 id=normalize_lccn(id);-- get canonical form (no whitespace, hyphens, forward slashes)
 locallen=id:len();-- get the length of the LCCN

 if8==lenthen
 ifid:match("[^%d]")then-- if LCCN has anything but digits (nil if only digits)
 err_flag=set_message('err_bad_lccn');-- set an error message
 end
 elseif9==lenthen-- LCCN should be adddddddd
 ifnil==id:match("%l%d%d%d%d%d%d%d%d")then-- does it match our pattern?
 err_flag=set_message('err_bad_lccn');-- set an error message
 end
 elseif10==lenthen-- LCCN should be aadddddddd or dddddddddd
 ifid:match("[^%d]")then-- if LCCN has anything but digits (nil if only digits) ...
 ifnil==id:match("^%l%l%d%d%d%d%d%d%d%d")then-- ... see if it matches our pattern
 err_flag=set_message('err_bad_lccn');-- no match, set an error message
 end
 end
 elseif11==lenthen-- LCCN should be aaadddddddd or adddddddddd
 ifnot(id:match("^%l%l%l%d%d%d%d%d%d%d%d")orid:match("^%l%d%d%d%d%d%d%d%d%d%d"))then-- see if it matches one of our patterns
 err_flag=set_message('err_bad_lccn');-- no match, set an error message
 end
 elseif12==lenthen-- LCCN should be aadddddddddd
 ifnotid:match("^%l%l%d%d%d%d%d%d%d%d%d%d")then-- see if it matches our pattern
 err_flag=set_message('err_bad_lccn');-- no match, set an error message
 end
 else
 err_flag=set_message('err_bad_lccn');-- wrong length, set an error message
 end

 ifnotis_set(err_flag)andnil~=lccn:find('%s')then
 err_flag=set_message('err_bad_lccn');-- lccn contains a space, set an error message
 end

 ifis_set(err_flag)then
 options.coins_list_t['LCCN']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=lccn,separator=handler.separator,encode=handler.encode});
 end


 --[[--------------------------< M E D R X I V >-----------------------------------------------------------------

 Format medRxiv ID and do simple error checking. Similar to later bioRxiv IDs, medRxiv IDs are prefixed with a
 yyyy.mm.dd. date and suffixed with an optional version identifier. Ealiest date accepted is 2020年01月01日

 The medRxiv ID is a date followed by an eight-digit number followed by an optional version indicator 'v' and one or more digits:
 	https://www.medrxiv.org/content/10.1101/2020.11.16.20232009v2 -> 10.1101/2020.11.16.20232009v2

 ]]

 localfunctionmedrxiv(options)
 localid=options.id;
 localhandler=options.handler;
 localerr_msg_flag=true;-- flag; assume that there will be an error

 localpatterns={
 '^%d%d%d%d%d%d%d%d$',-- simple 8-digit identifier; these should be relatively rare
 '^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%d%d%dv%d+$',-- y.m.d. date + 8-digit identifier + version (2020年01月01日 and later)
 '^10%.1101/(20%d%d)%.(%d%d)%.(%d%d)%.%d%d%d%d%d%d%d%d$',-- y.m.d. date + 8-digit identifier (2020年01月01日 and later)
 }

 for_,patterninipairs(patterns)do-- spin through the patterns looking for a match
 ifid:match(pattern)then
 localy,m,d=id:match(pattern);-- found a match, attempt to get year, month and date from the identifier

 ifmthen-- m is nil when id is the 8-digit form
 ifnotis_valid_rxiv_date(y,m,d,'b')then-- validate the encoded date; 'b' for medrxiv limit
 break;-- date fail; break out early so we don't unset the error message
 end
 end
 err_msg_flag=nil;-- we found a match so unset the error message
 break;-- and done
 end
 end-- <err_msg_flag> remains set here when no match

 iferr_msg_flagthen
 options.coins_list_t['MEDRXIV']=nil;-- when error, unset so not included in COinS
 set_message('err_bad_medrxiv');-- and set the error message
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,
 encode=handler.encode,access=handler.access});
 end


 --[[--------------------------< M R >--------------------------------------------------------------------------

 A seven digit number; if not seven digits, zero-fill leading digits to make seven digits.

 ]]

 localfunctionmr(options)
 localid=options.id;
 localhandler=options.handler;
 localid_num;
 localid_len;

 id_num=id:match('^[Mm][Rr](%d+)$');-- identifier with mr prefix

 ifis_set(id_num)then
 set_message('maint_mr_format');-- add maint cat
 else-- plain number without mr prefix
 id_num=id:match('^%d+$');-- if here id is all digits
 end

 id_len=id_numandid_num:len()or0;
 if(7>=id_len)and(0~=id_len)then
 id=string.rep('0',7-id_len)..id_num;-- zero-fill leading digits
 else
 set_message('err_bad_mr');-- set an error message
 options.coins_list_t['MR']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode});
 end


 --[[--------------------------< O C L C >----------------------------------------------------------------------

 Validate and format an OCLC ID. https://www.oclc.org/batchload/controlnumber.en.html {{dead link}}
 archived at: https://web.archive.org/web/20161228233804/https://www.oclc.org/batchload/controlnumber.en.html

 ]]

 localfunctionoclc(options)
 localid=options.id;
 localhandler=options.handler;
 localnumber;

 ifid:match('^ocm%d%d%d%d%d%d%d%d$')then-- ocm prefix and 8 digits; 001 field (12 characters)
 number=id:match('ocm(%d+)');-- get the number
 elseifid:match('^ocn%d%d%d%d%d%d%d%d%d$')then-- ocn prefix and 9 digits; 001 field (12 characters)
 number=id:match('ocn(%d+)');-- get the number
 elseifid:match('^on%d%d%d%d%d%d%d%d%d%d+$')then-- on prefix and 10 or more digits; 001 field (12 characters)
 number=id:match('^on(%d%d%d%d%d%d%d%d%d%d+)$');-- get the number
 elseifid:match('^%(OCoLC%)[1-9]%d*$')then-- (OCoLC) prefix and variable number digits; no leading zeros; 035 field
 number=id:match('%(OCoLC%)([1-9]%d*)');-- get the number
 if9<number:len()then
 number=nil;-- constrain to 1 to 9 digits; change this when OCLC issues 10-digit numbers
 end
 elseifid:match('^%d+$')then-- no prefix
 number=id;-- get the number
 iftonumber(id)>handler.id_limitthen
 number=nil;-- unset when id value exceeds the limit
 end
 end

 ifnumberthen-- proper format
 id=number;-- exclude prefix, if any, from external link
 else
 set_message('err_bad_oclc')-- add an error message if the id is malformed
 options.coins_list_t['OCLC']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode});
 end


 --[[--------------------------< O P E N L I B R A R Y >--------------------------------------------------------

 Formats an OpenLibrary link, and checks for associated errors.

 ]]

 localfunctionopenlibrary(options)
 localid=options.id;
 localaccess=options.access;
 localhandler=options.handler;
 localident,code=id:gsub('^OL',''):match("^(%d+([AMW]))$");-- strip optional OL prefix followed immediately by digits followed by 'A', 'M', or 'W';
 localerr_flag;
 localprefix={-- these are appended to the handler.prefix according to code
 ['A']='authors/OL',
 ['M']='books/OL',
 ['W']='works/OL',
 ['X']='OL'-- not a code; spoof when 'code' in id is invalid
 };

 ifnotidentthen
 code='X';-- no code or id completely invalid
 ident=id;-- copy id to ident so that we display the flawed identifier
 err_flag=set_message('err_bad_ol');
 end

 ifnotis_set(err_flag)then
 options.coins_list_t['OL']=handler.prefix..prefix[code]..ident;-- experiment for ol coins
 else
 options.coins_list_t['OL']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix..prefix[code],
 id=ident,separator=handler.separator,encode=handler.encode,
 access=access});
 end


 --[[--------------------------< O S T I >----------------------------------------------------------------------

 Format OSTI and do simple error checking. OSTIs are sequential numbers beginning at 1 and counting up. This
 code checks the OSTI to see that it contains only digits and is less than test_limit specified in the configuration;
 the value in test_limit will need to be updated periodically as more OSTIs are issued.

 NB. 1018 is the lowest OSTI number found in the wild (so far) and resolving OK on the OSTI site

 ]]

 localfunctionosti(options)
 localid=options.id;
 localaccess=options.access;
 localhandler=options.handler;

 ifid:match("[^%d]")then-- if OSTI has anything but digits
 set_message('err_bad_osti');-- set an error message
 options.coins_list_t['OSTI']=nil;-- when error, unset so not included in COinS
 else-- OSTI is only digits
 localid_num=tonumber(id);-- convert id to a number for range testing
 if1018>id_numorhandler.id_limit<id_numthen-- if OSTI is outside test limit boundaries
 set_message('err_bad_osti');-- set an error message
 options.coins_list_t['OSTI']=nil;-- when error, unset so not included in COinS
 end
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=access});
 end


 --[[--------------------------< P M C >------------------------------------------------------------------------

 Format a PMC, do simple error checking, and check for embargoed articles.

 The embargo parameter takes a date for a value. If the embargo date is in the future the PMC identifier will not
 be linked to the article. If the embargo date is today or in the past, or if it is empty or omitted, then the
 PMC identifier is linked to the article through the link at cfg.id_handlers['PMC'].prefix.

 PMC embargo date testing is done in function is_embargoed () which is called earlier because when the citation
 has |pmc=<value> but does not have a |url= then |title= is linked with the PMC link. Function is_embargoed ()
 returns the embargo date if the PMC article is still embargoed, otherwise it returns an empty string.

 PMCs are sequential numbers beginning at 1 and counting up. This code checks the PMC to see that it contains only digits and is less
 than test_limit; the value in local variable test_limit will need to be updated periodically as more PMCs are issued.

 ]]

 localfunctionpmc(options)
 localid=options.id;
 localembargo=options.Embargo;-- TODO: lowercase?
 localhandler=options.handler;
 localerr_flag;
 localid_num;
 localtext;

 id_num=id:match('^[Pp][Mm][Cc](%d+)$');-- identifier with PMC prefix

 ifis_set(id_num)then
 set_message('maint_pmc_format');
 else-- plain number without PMC prefix
 id_num=id:match('^%d+$');-- if here id is all digits
 end

 ifis_set(id_num)then-- id_num has a value so test it
 id_num=tonumber(id_num);-- convert id_num to a number for range testing
 if1>id_numorhandler.id_limit<id_numthen-- if PMC is outside test limit boundaries
 err_flag=set_message('err_bad_pmc');-- set an error message
 else
 id=tostring(id_num);-- make sure id is a string
 end
 else-- when id format incorrect
 err_flag=set_message('err_bad_pmc');-- set an error message
 end

 ifis_set(embargo)andis_set(is_embargoed(embargo))then-- is PMC is still embargoed?
 text=table.concat(-- still embargoed so no external link
 {
 make_wikilink(label_link_make(handler),handler.label),
 handler.separator,
 id,
 });
 else
 text=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,-- no embargo date or embargo has expired, ok to link to article
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=handler.access,
 auto_link=noterr_flagand'pmc'ornil-- do not auto-link when PMC has error
 });
 end

 iferr_flagthen
 options.coins_list_t['PMC']=nil;-- when error, unset so not included in COinS
 end

 returntext;
 end


 --[[--------------------------< P M I D >----------------------------------------------------------------------

 Format PMID and do simple error checking. PMIDs are sequential numbers beginning at 1 and counting up. This
 code checks the PMID to see that it contains only digits and is less than test_limit; the value in local variable
 test_limit will need to be updated periodically as more PMIDs are issued.

 ]]

 localfunctionpmid(options)
 localid=options.id;
 localhandler=options.handler;

 ifid:match("[^%d]")then-- if PMID has anything but digits
 set_message('err_bad_pmid');-- set an error message
 options.coins_list_t['PMID']=nil;-- when error, unset so not included in COinS
 else-- PMID is only digits
 localid_num=tonumber(id);-- convert id to a number for range testing
 if1>id_numorhandler.id_limit<id_numthen-- if PMID is outside test limit boundaries
 set_message('err_bad_pmid');-- set an error message
 options.coins_list_t['PMID']=nil;-- when error, unset so not included in COinS
 end
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode});
 end


 --[[--------------------------< R F C >------------------------------------------------------------------------

 Format RFC and do simple error checking. RFCs are sequential numbers beginning at 1 and counting up. This
 code checks the RFC to see that it contains only digits and is less than test_limit specified in the configuration;
 the value in test_limit will need to be updated periodically as more RFCs are issued.

 An index of all RFCs is here: https://tools.ietf.org/rfc/

 ]]

 localfunctionrfc(options)
 localid=options.id;
 localhandler=options.handler;

 ifid:match("[^%d]")then-- if RFC has anything but digits
 set_message('err_bad_rfc');-- set an error message
 options.coins_list_t['RFC']=nil;-- when error, unset so not included in COinS
 else-- RFC is only digits
 localid_num=tonumber(id);-- convert id to a number for range testing
 if1>id_numorhandler.id_limit<id_numthen-- if RFC is outside test limit boundaries
 set_message('err_bad_rfc');-- set an error message
 options.coins_list_t['RFC']=nil;-- when error, unset so not included in COinS
 end
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=handler.access});
 end


 --[[--------------------------< S 2 C I D >--------------------------------------------------------------------

 Format an S2CID, do simple error checking

 S2CIDs are sequential numbers beginning at 1 and counting up. This code checks the S2CID to see that it is only
 digits and is less than test_limit; the value in local variable test_limit will need to be updated periodically
 as more S2CIDs are issued.

 ]]

 localfunctions2cid(options)
 localid=options.id;
 localaccess=options.access;
 localhandler=options.handler;
 localid_num;
 localtext;

 id_num=id:match('^[1-9]%d*$');-- id must be all digits; must not begin with 0; no open access flag

 ifis_set(id_num)then-- id_num has a value so test it
 id_num=tonumber(id_num);-- convert id_num to a number for range testing
 ifhandler.id_limit<id_numthen-- if S2CID is outside test limit boundaries
 set_message('err_bad_s2cid');-- set an error message
 options.coins_list_t['S2CID']=nil;-- when error, unset so not included in COinS
 end
 else-- when id format incorrect
 set_message('err_bad_s2cid');-- set an error message
 options.coins_list_t['S2CID']=nil;-- when error, unset so not included in COinS
 end

 text=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=access});

 returntext;
 end


 --[[--------------------------< S B N >------------------------------------------------------------------------

 9-digit form of ISBN-10; uses same check-digit validation when SBN is prefixed with an additional '0' to make 10 digits

 sbn value not made part of COinS metadata because we don't have a url or isn't a COinS-defined identifier (rft.xxx)
 or an identifier registered at info-uri.info (info:)

 ]]

 localfunctionsbn(options)
 localid=options.id;
 localignore_invalid=options.accept;
 localhandler=options.handler;
 localfunctionreturn_result(check,err_type)-- local function to handle the various returns
 localSBN=internal_link_id({link=handler.link,label=handler.label,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator});
 ifnotignore_invalidthen-- if not ignoring SBN errors
 ifnotcheckthen
 options.coins_list_t['SBN']=nil;-- when error, unset so not included in COinS; not really necessary here because sbn not made part of COinS
 set_message('err_bad_sbn',{err_type});-- display an error message
 returnSBN;
 end
 else
 set_message('maint_isbn_ignore');-- add a maint category even when there is no error (ToDo: Possibly switch to separate message for SBNs only)
 end
 returnSBN;
 end

 ifid:match('[^%s-0-9X]')then
 returnreturn_result(false,cfg.err_msg_supl.char);-- fail if SBN contains anything but digits, hyphens, or the uppercase X
 end

 localident=id:gsub('[%s-]','');-- remove hyphens and whitespace; they interfere with the rest of the tests

 if9~=ident:len()then
 returnreturn_result(false,cfg.err_msg_supl.length);-- fail if incorrect length
 end

 ifident:match('^%d*X?$')==nilthen
 returnreturn_result(false,cfg.err_msg_supl.form);-- fail if SBN has 'X' anywhere but last position
 end

 returnreturn_result(is_valid_isxn('0'..ident,10),cfg.err_msg_supl.check);
 end


 --[[--------------------------< S S R N >----------------------------------------------------------------------

 Format an SSRN, do simple error checking

 SSRNs are sequential numbers beginning at 100? and counting up. This code checks the SSRN to see that it is
 only digits and is greater than 99 and less than test_limit; the value in local variable test_limit will need
 to be updated periodically as more SSRNs are issued.

 ]]

 localfunctionssrn(options)
 localid=options.id;
 localhandler=options.handler;
 localid_num;
 localtext;

 id_num=id:match('^%d+$');-- id must be all digits

 ifis_set(id_num)then-- id_num has a value so test it
 id_num=tonumber(id_num);-- convert id_num to a number for range testing
 if100>id_numorhandler.id_limit<id_numthen-- if SSRN is outside test limit boundaries
 set_message('err_bad_ssrn');-- set an error message
 options.coins_list_t['SSRN']=nil;-- when error, unset so not included in COinS
 end
 else-- when id format incorrect
 set_message('err_bad_ssrn');-- set an error message
 options.coins_list_t['SSRN']=nil;-- when error, unset so not included in COinS
 end

 text=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode,access=options.access});

 returntext;
 end


 --[[--------------------------< U S E N E T _ I D >------------------------------------------------------------

 Validate and format a usenet message id. Simple error checking, looks for 'id-left@id-right' not enclosed in
 '<' and/or '>' angle brackets.

 ]]

 localfunctionusenet_id(options)
 localid=options.id;
 localhandler=options.handler;

 localtext=external_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode})

 ifnotid:match('^.+@.+$')ornotid:match('^[^<].*[^>]$')then-- doesn't have '@' or has one or first or last character is '< or '>'
 set_message('err_bad_usenet_id')-- add an error message if the message id is invalid
 options.coins_list_t['USENETID']=nil;-- when error, unset so not included in COinS
 end

 returntext;
 end


 --[[--------------------------< Z B L >-----------------------------------------------------------------------

 A numerical identifier in the form nnnn.nnnnn - leading zeros in the first quartet optional

 format described here: http://emis.mi.sanu.ac.rs/ZMATH/zmath/en/help/search/

 temporary format is apparently eight digits. Anything else is an error

 ]]

 localfunctionzbl(options)
 localid=options.id;
 localhandler=options.handler;

 ifid:match('^%d%d%d%d%d%d%d%d$')then-- is this identifier using temporary format?
 set_message('maint_zbl');-- yes, add maint cat
 elseifnotid:match('^%d?%d?%d?%d%.%d%d%d%d%d$')then-- not temporary, is it normal format?
 set_message('err_bad_zbl');-- no, set an error message
 options.coins_list_t['ZBL']=nil;-- when error, unset so not included in COinS
 end

 returnexternal_link_id({link=handler.link,label=handler.label,q=handler.q,redirect=handler.redirect,
 prefix=handler.prefix,id=id,separator=handler.separator,encode=handler.encode});
 end


 --============================<< I N T E R F A C E F U N C T I O N S >>==========================================

 --[[--------------------------< E X T R A C T _ I D S >------------------------------------------------------------

 Populates ID table from arguments using configuration settings. Loops through cfg.id_handlers and searches args for
 any of the parameters listed in each cfg.id_handlers['...'].parameters. If found, adds the parameter and value to
 the identifier list. Emits redundant error message if more than one alias exists in args

 ]]

 localfunctionextract_ids(args)
 localid_list={};-- list of identifiers found in args
 fork,vinpairs(cfg.id_handlers)do-- k is uppercase identifier name as index to cfg.id_handlers; e.g. cfg.id_handlers['ISBN'], v is a table
 v=select_one(args,v.parameters,'err_redundant_parameters');-- v.parameters is a table of aliases for k; here we pick one from args if present
 ifis_set(v)thenid_list[k]=v;end-- if found in args, add identifier to our list
 end
 returnid_list;
 end


 --[[--------------------------< E X T R A C T _ I D _ A C C E S S _ L E V E L S >--------------------------------------

 Fetches custom id access levels from arguments using configuration settings. Parameters which have a predefined access
 level (e.g. arxiv) do not use this function as they are directly rendered as free without using an additional parameter.

 returns a table of k/v pairs where k is same as the identifier's key in cfg.id_handlers and v is the assigned (valid) keyword

 access-level values must match the case used in cfg.keywords_lists['id-access'] (lowercase unless there is some special reason for something else)

 ]]

 localfunctionextract_id_access_levels(args,id_list)
 localid_accesses_list={};
 fork,vinpairs(cfg.id_handlers)do
 localaccess_param=v.custom_access;-- name of identifier's access-level parameter
 ifis_set(access_param)then
 localaccess_level=args[access_param];-- get the assigned value if there is one
 ifis_set(access_level)then
 ifnotin_array(access_level,cfg.keywords_lists['id-access'])then-- exact match required
 set_message('err_invalid_param_val',{access_param,access_level});
 access_level=nil;-- invalid so unset
 end
 ifnotis_set(id_list[k])then-- identifier access-level must have a matching identifier
 set_message('err_param_access_requires_param',{k:lower()});-- parameter name is uppercase in cfg.id_handlers (k); lowercase for error message
 end
 id_accesses_list[k]=cfg.keywords_xlate[access_level];-- get translated keyword
 end
 end
 end
 returnid_accesses_list;
 end


 --[[--------------------------< B U I L D _ I D _ L I S T >----------------------------------------------------

 render the identifiers into a sorted sequence table

 <ID_list_coins_t> is a table of k/v pairs where k is same as key in cfg.id_handlers and v is the assigned value
 <options_t> is a table of various k/v option pairs provided in the call to new_build_id_list();
 	modified by	this function and passed to all identifier rendering functions
 <access_levels_t> is a table of k/v pairs where k is same as key in cfg.id_handlers and v is the assigned value (if valid)

 returns a sequence table of sorted (by hkey - 'handler' key) rendered identifier strings

 ]]

 localfunctionbuild_id_list(ID_list_coins_t,options_t,access_levels_t)
 localID_list_t={};
 localaccept;
 localfunc_map={--function map points to functions associated with hkey identifier
 ['ARXIV']=arxiv,
 ['ASIN']=asin,
 ['BIBCODE']=bibcode,
 ['BIORXIV']=biorxiv,
 ['CITESEERX']=citeseerx,
 ['DOI']=doi,
 ['EISSN']=issn,
 ['HDL']=hdl,
 ['ISBN']=isbn,
 ['ISMN']=ismn,
 ['ISSN']=issn,
 ['JFM']=jfm,
 ['JSTOR']=jstor,
 ['LCCN']=lccn,
 ['MEDRXIV']=medrxiv,
 ['MR']=mr,
 ['OCLC']=oclc,
 ['OL']=openlibrary,
 ['OSTI']=osti,
 ['PMC']=pmc,
 ['PMID']=pmid,
 ['RFC']=rfc,
 ['S2CID']=s2cid,
 ['SBN']=sbn,
 ['SSRN']=ssrn,
 ['USENETID']=usenet_id,
 ['ZBL']=zbl,
 }

 forhkey,vinpairs(ID_list_coins_t)do
 v,accept=has_accept_as_written(v);-- remove accept-as-written markup if present; accept is boolean true when markup removed; false else
 -- every function gets the options table with value v and accept boolean
 options_t.hkey=hkey;-- ~/Configuration handler key
 options_t.id=v;-- add that identifier value to the options table
 options_t.accept=accept;-- add the accept boolean flag
 options_t.access=access_levels_t[hkey];-- add the access level for those that have an |<identifier-access= parameter
 options_t.handler=cfg.id_handlers[hkey];
 options_t.coins_list_t=ID_list_coins_t;-- pointer to ID_list_coins_t; for |asin= and |ol=; also to keep erroneous values out of the citation's metadata
 options_t.coins_list_t[hkey]=v;-- id value without accept-as-written markup for metadata

 ifoptions_t.handler.accessandnotin_array(options_t.handler.access,cfg.keywords_lists['id-access'])then
 error(cfg.messages['unknown_ID_access']..options_t.handler.access);-- here when handler access key set to a value not listed in list of allowed id access keywords
 end

 iffunc_map[hkey]then
 localid_text=func_map[hkey](options_t);-- call the function to get identifier text and any error message
 table.insert(ID_list_t,{hkey,id_text});-- add identifier text to the output sequence table
 else
 error(cfg.messages['unknown_ID_key']..hkey);-- here when func_map doesn't have a function for hkey
 end
 end

 localfunctioncomp(a,b)-- used by following table.sort()
 returna[1]:lower()<b[1]:lower();-- sort by hkey
 end

 table.sort(ID_list_t,comp);-- sequence table of tables sort	
 fork,vinipairs(ID_list_t)do-- convert sequence table of tables to simple sequence table of strings
 ID_list_t[k]=v[2];-- v[2] is the identifier rendering from the call to the various functions in func_map{}
 end

 returnID_list_t;
 end


 --[[--------------------------< O P T I O N S _ C H E C K >----------------------------------------------------

 check that certain option parameters have their associated identifier parameters with values

 <ID_list_coins_t> is a table of k/v pairs where k is same as key in cfg.id_handlers and v is the assigned value
 <ID_support_t> is a sequence table of tables created in citation0() where each subtable has four elements:
 	[1] is the support parameter's assigned value; empty string if not set
 	[2] is a text string same as key in cfg.id_handlers
 	[3] is cfg.error_conditions key used to create error message
 	[4] is original ID support parameter name used to create error message

 returns nothing; on error emits an appropriate error message

 ]]

 localfunctionoptions_check(ID_list_coins_t,ID_support_t)
 for_,vinipairs(ID_support_t)do
 ifis_set(v[1])andnotID_list_coins_t[v[2]]then-- when support parameter has a value but matching identifier parameter is missing or empty
 set_message(v[3],(v[4]));-- emit the appropriate error message
 end
 end
 end


 --[[--------------------------< I D E N T I F I E R _ L I S T S _ G E T >--------------------------------------

 Creates two identifier lists: a k/v table of identifiers and their values to be used locally and for use in the
 COinS metadata, and a sequence table of the rendered identifier strings that will be included in the rendered
 citation.

 ]]

 localfunctionidentifier_lists_get(args_t,options_t,ID_support_t)
 localID_list_coins_t=extract_ids(args_t);-- get a table of identifiers and their values for use locally and for use in COinS
 options_check(ID_list_coins_t,ID_support_t);-- ID support parameters must have matching identifier parameters 
 localID_access_levels_t=extract_id_access_levels(args_t,ID_list_coins_t);-- get a table of identifier access levels
 localID_list_t=build_id_list(ID_list_coins_t,options_t,ID_access_levels_t);-- get a sequence table of rendered identifier strings

 returnID_list_t,ID_list_coins_t;-- return the tables
 end


 --[[--------------------------< S E T _ S E L E C T E D _ M O D U L E S >--------------------------------------

 Sets local cfg table and imported functions table to same (live or sandbox) as that used by the other modules.

 ]]

 localfunctionset_selected_modules(cfg_table_ptr,utilities_page_ptr)
 cfg=cfg_table_ptr;

 has_accept_as_written=utilities_page_ptr.has_accept_as_written;-- import functions from select Module:Citation/CS1/Utilities module
 is_set=utilities_page_ptr.is_set;
 in_array=utilities_page_ptr.in_array;
 set_message=utilities_page_ptr.set_message;
 select_one=utilities_page_ptr.select_one;
 substitute=utilities_page_ptr.substitute;
 make_wikilink=utilities_page_ptr.make_wikilink;

 z=utilities_page_ptr.z;-- table of tables in Module:Citation/CS1/Utilities
 end


 --[[--------------------------< E X P O R T E D F U N C T I O N S >------------------------------------------
 ]]

 return{
 auto_link_urls=auto_link_urls,-- table of identifier URLs to be used when auto-linking |title=

 identifier_lists_get=identifier_lists_get,-- experiment to replace individual calls to build_id_list(), extract_ids, extract_id_access_levels
 is_embargoed=is_embargoed;
 set_selected_modules=set_selected_modules;
 }