require ('strict');  
----------------------------< F O R W A R D D E C L A R A T I O N S >--------------------------------------  
each of these counts against the Lua upvalue limit  
local validation; -- functions in Module:Citation/CS1/Date_validation  
local utilities; -- functions in Module:Citation/CS1/Utilities
local z = {}; -- table of tables in Module:Citation/CS1/Utilities  
local identifiers; -- functions and tables in Module:Citation/CS1/Identifiers
local metadata; -- functions in Module:Citation/CS1/COinS
local cfg = {}; -- table of configuration tables that are defined in Module:Citation/CS1/Configuration
local whitelist = {}; -- table of tables listing valid template parameter names; defined in Module:Citation/CS1/Whitelist  
--------------------< 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  
local added_deprecated_cat; -- Boolean flag so that the category is added only once
local added_vanc_errs; -- Boolean flag so we only emit one Vancouver error / category
local added_generic_name_errs; -- Boolean flag so we only emit one generic name error / category and stop testing names once an error is encountered
local added_numeric_name_errs; -- Boolean flag so we only emit one numeric name error / category and stop testing names once an error is encountered
local added_numeric_name_maint; -- Boolean flag so we only emit one numeric name maint category and stop testing names once a category has been emitted
local Frame; -- holds the module's table
local is_preview_mode; -- true when article is in preview mode; false when using 'Preview page with this template' (previewing the module)
local is_sandbox; -- true when using sandbox modules to render citation  
----------------------------< F I R S T _ S E T >------------------------------------------------------------  
Locates and returns the first set value in a table of values where the order established in the table,
-to- (or top-to-bottom), is the order in which the values are evaluated. Returns nil if are set.  
This version replaces the original 'for _, val in pairs do' and a similar version that used ipairs. With the pairs
version the order of evaluation could not be guaranteed. With the ipairs version, a nil value would terminate
the for-loop before it reached the actual end of the list.  
local function first_set (list, count)
local i = 1;
while i <= count do -- loop through all items in list
if utilities.is_set( list[i] ) then
return list[i]; -- return the first set list member
end
i = i + 1; -- point to next
end
end  
----------------------------< A D D _ V A N C _ E R R O R >----------------------------------------------------  
Adds a single Vancouver system error message to the template's output regardless of how many error actually exist.
To prevent duplication, added_vanc_errs is nil until an error message is emitted.  
added_vanc_errs is a Boolean declared in page scope variables above  
local function add_vanc_error (source, position)
if added_vanc_errs then return end  
added_vanc_errs = true; -- note that we've added this category
utilities.set_message ('err_vancouver', {source, position});
end  
----------------------------< I S _ S C H E M E >------------------------------------------------------------  
does this thing that purports to be a URI scheme seem to be a valid scheme? The scheme is checked to see if it
is in agreement with http://tools.ietf.org/html/std66#section-3.1 which says:
Scheme names consist of a sequence of characters beginning with a
letter and followed by any combination of letters, digits, plus
("+"), period ("."), or hyphen ("-").  
returns true if it does, else false  
local function is_scheme (scheme)
return scheme and scheme:match ('^%a[%a%d%+%.%-]*:'); -- true if scheme is set and matches the pattern
end  
--[=[-------------------------< I S _ D O M A I N _ N A M E >--------------------------------------------------  
Does this thing that purports to be a domain name seem to be a valid domain name?  
Syntax defined here: http://tools.ietf.org/html/rfc1034#section-3.5
BNF defined here: https://tools.ietf.org/html/rfc4234
Single character names are generally reserved; see https://tools.ietf.org/html/draft-ietf-dnsind-iana-dns-01#page-15;
see also Single-letter second-level domain
list of TLDs: https://www.iana.org/domains/root/db  
RFC 952 (modified by RFC 1123) requires the first and last character of a hostname to be a letter or a digit. Between
the first and last characters the name may use letters, digits, and the hyphen.  
Also allowed are IPv4 addresses. IPv6 not supported  
domain is expected to be stripped of any path so that the last character in the last character of the TLD. tld
is two or more alpha characters. Any preceding '//' (from splitting a URL with a scheme) will be stripped
here. Perhaps not necessary but retained in case it is necessary for IPv4 dot decimal.  
There are several tests:
the first character of the whole domain name including subdomains must be a letter or a digit
internationalized domain name (ASCII characters with .xn-- ASCII Compatible Encoding (ACE) prefix xn-- in the TLD) see https://tools.ietf.org/html/rfc3490
single-letter/digit second-level domains in the .org, .cash, and .today TLDs
q, x, and z SL domains in the .com TLD
i and q SL domains in the .net TLD
single-letter SL domains in the ccTLDs (where the ccTLD is two letters)
two-character SL domains in gTLDs (where the gTLD is two or more letters)
three-plus-character SL domains in gTLDs (where the gTLD is two or more letters)
IPv4 dot-decimal address format; TLD not allowed  
returns true if domain appears to be a proper name and TLD or IPv4 address, else false  
]=]  
local function is_domain_name (domain)
if not domain then
return false; -- if not set, abandon
end  
domain = domain:gsub ('^//', ''); -- strip '//' from domain name if present; done here so we only have to do it once  
if not domain:match ('^[%w]') then -- first character must be letter or digit
return false;
end  
if domain:match ('^%a+:') then -- hack to detect things that look like s:Page:Title where Page: is namespace at Wikisource
return false;
end  
local patterns = { -- patterns that look like URLs
'%f[%w][%w][%w%-]+[%w]%.%a%a+$', -- three or more character hostname.hostname or hostname.tld
'%f[%w][%w][%w%-]+[%w]%.xn%-%-[%w]+$', -- internationalized domain name with ACE prefix
'%f[%a][qxz]%.com$', -- assigned one character .com hostname (x.com times out 2015-12-10)
'%f[%a][iq]%.net$', -- assigned one character .net hostname (q.net registered but not active 2015-12-10)
'%f[%w][%w]%.%a%a$', -- one character hostname and ccTLD (2 chars)
'%f[%w][%w][%w]%.%a%a+$', -- two character hostname and TLD
'^%d%d?%d?%.%d%d?%d?%.%d%d?%d?%.%d%d?%d?', -- IPv4 address
'[%a%d]+%:?' -- IPv6 address
}  
for _, pattern in ipairs (patterns) do -- loop through the patterns list
if domain:match (pattern) then
return true; -- if a match then we think that this thing that purports to be a URL is a URL
end
end  
for _, d in ipairs (cfg.single_letter_2nd_lvl_domains_t) do -- look for single letter second level domain names for these top level domains
if domain:match ('%f[%w][%w]%.' .. d) then
return true
end
end
return false; -- no matches, we don't know what this thing is
end  
----------------------------< I S _ U R L >------------------------------------------------------------------  
returns true if the scheme and domain parts of a URL appear to be a valid URL; else false.  
This function is the last step in the validation process. This function is separate because there are cases that
are not covered by split_url, for example is_parameter_ext_wikilink which is looking for bracketted external
wikilinks.  
local function is_url (scheme, domain)
if utilities.is_set (scheme) then -- if scheme is set check it and domain