Unicode group, or the stripmarker that was detected along with its position (or,
for multi-byte characters, the position of its first byte) in the parameter value.  
local function has_invisible_chars (param, v)
local position = ''; -- position of invisible char or starting position of stripmarker
local capture; -- used by stripmarker detection to hold name of the stripmarker
local stripmarker; -- boolean set true when a stripmarker is found  
capture = string.match (v, '[%w%p ]*'); -- test for values that are simple ASCII text and bypass other tests if true
if capture == v then -- if same there are no Unicode characters
return;
end  
for _, invisible_char in ipairs (cfg.invisible_chars) do
local char_name = invisible_char[1]; -- the character or group name
local pattern = invisible_char[2]; -- the pattern used to find it
position, _, capture = mw.ustring.find (v, pattern); -- see if the parameter value contains characters that match the pattern  
if position and (cfg.invisible_defs.zwj == capture) then -- if we found a zero-width joiner character
if mw.ustring.find (v, cfg.indic_script) then -- it's ok if one of the Indic scripts
position = nil; -- unset position
elseif cfg.emoji_t[mw.ustring.codepoint (v, position+1)] then -- is zwj followed by a character listed in emoji{}?
position = nil; -- unset position
end
end  
if position then
if 'nowiki' == capture or 'math' == capture or -- nowiki and math stripmarkers (not an error condition)
('templatestyles' == capture and utilities.in_array (param, {'id', 'quote'})) then -- templatestyles stripmarker allowed in these parameters
stripmarker = true; -- set a flag
elseif true == stripmarker and cfg.invisible_defs.del == capture then -- because stripmakers begin and end with the delete char, assume that we've found one end of a stripmarker
position = nil; -- unset
else
local err_msg;
if capture and not (cfg.invisible_defs.del == capture or cfg.invisible_defs.zwj == capture) then
err_msg = capture .. ' ' .. char_name;
else
err_msg = char_name .. ' ' .. 'character';
end  
utilities.set_message ('err_invisible_char', {err_msg, utilities.wrap_style ('parameter', param), position}); -- add error message
return; -- and done with this parameter
end
end
end
end  
---------------------< A R G U M E N T _ W R A P P E R >----------------------  
Argument wrapper. This function provides support for argument mapping defined
in the configuration file so that multiple names can be transparently aliased to
single internal variable.  
local function argument_wrapper ( args )
local origin = {};  
return setmetatable({
ORIGIN = function ( self, k )
local dummy = self[k]; -- force the variable to be loaded.
return origin[k];
end
},
{
__index = function ( tbl, k )
if origin[k] ~= nil then
return nil;
end  
local args, list, v = args, cfg.aliases[k];  
if type( list ) == 'table' then
v, origin[k] = utilities.select_one ( args, list, 'err_redundant_parameters' );
if origin[k] == nil then
origin[k] = ''; -- Empty string, not nil
end
elseif list ~= nil then
v, origin[k] = args[list], list;
else
-- maybe let through instead of raising an error?
-- v, origin[k] = args[k], k;
error( cfg.messages['unknown_argument_map'] .. ': ' .. k);
end  
-- Empty strings, not nil;
if v == nil then
v = '';
origin[k] = '';
end  
tbl = rawset( tbl, k, v );
return v;
end,
});
end  
----------------------------< N O W R A P _ D A T E >-------------------------  
When date is YYYY-MM-DD format wrap in nowrap span: <span ...>YYYY-MM-DD</span>.
When date is DD MMMM YYYY or is MMMM DD, YYYY then wrap in nowrap span:
<span ...>DD MMMM</span> YYYY or <span ...>MMMM DD,</span> YYYY  
DOES NOT yet support MMMM YYYY or any of the date ranges.  
local function nowrap_date (date)
local cap = '';
local cap2 = '';  
if date:match("^%d%d%d%d%-%d%d%-%d%d$") then
date = utilities.substitute (cfg.presentation['nowrap1'], date);  
elseif date:match("^%a+%s*%d%d?,%s+%d%d%d%d$") or date:match ("^%d%d?%s*%a+%s+%d%d%d%d$") then
cap, cap2 = string.match (date, "^(.*)%s+(%d%d%d%d)$");
date = utilities.substitute (cfg.presentation['nowrap2'], {cap, cap2});
end  
return date;
end  
--type=<default value>) for those templates that have defaults. Also handles the
special case where it is desirable to omit the title type from the rendered citation
(|type=).  
local function set_titletype (cite_class, title_type)
if utilities.is_set (title_type) then
if '' == cfg.keywords_xlate[title_type] then
title_type = ''; -- if |type= then type parameter not displayed
end
return title_type; -- if |type= has been set to any other value use that value
end  
return cfg.title_types [cite_class] or ''; -- set template's default title type; else empty string for concatenation
end  
----------------------------< S A F E _ J O I N >-----------------------------  
Joins a sequence of strings together while checking for duplicate separation characters.  
local function safe_join( tbl, duplicate_char )
local f = {}; -- create a function table appropriate to type of 'duplicate character'
if 1 == #duplicate_char then -- for single byte ASCII characters use the string library functions
f.gsub = string.gsub
f.match = string.match
f.sub = string.sub
else -- for multi-byte characters use the ustring library functions
f.gsub = mw.ustring.gsub
f.match = mw.ustring.match
f.sub = mw.ustring.sub
end  
local str = ''; -- the output string
local comp = ''; -- what does 'comp' mean?
local end_chr = '';
local trim;
for _, value in ipairs( tbl ) do
if value == nil then value = ''; end  
if str == '' then -- if output string is empty
str = value; -- assign value to it (first time through the loop)
elseif value ~= '' then
if value:sub(1, 1) == '<' then -- special case of values enclosed in spans and other markup.
comp = value:gsub( "%b<>", "" ); -- remove HTML markup (<span>string</span> -> string)
else
comp = value;
end
-- typically duplicate_char is sepc
if f.sub(comp, 1, 1) == duplicate_char then -- is first character same as duplicate_char? why test first character?
-- Because individual string segments often (always?) begin with terminal punct for the
-- preceding segment: 'First element' .. 'sepc next element' .. etc.?
trim = false;
end_chr = f.sub(str, -1, -1); -- get the last character of the output string
-- str = str .. "<HERE(enchr=" .. end_chr .. ")" -- debug stuff?
if end_chr == duplicate_char then -- if same as separator
str = f.sub(str, 1, -2); -- remove it
elseif end_chr == "'" then -- if it might be wiki-markup
if f.sub(str, -3, -1) == duplicate_char .. "*" then -- if last three chars of str are sepc*
str = f.sub(str, 1, -4) .. "*"; -- remove them and add back *
elseif f.sub(str, -5, -1) == duplicate_char .. "]]*" then -- if last five chars of str are sepc]]*
trim = true; -- why? why do this and next differently from previous?
elseif f.sub(str, -4, -1) == duplicate_char .. "]*" then -- if last four chars of str are sepc]*
trim = true; -- same question
end
elseif end_chr == "]" then -- if it might be wiki-markup
if f.sub(str, -3, -1) == duplicate_char .. "]]" then -- if last three chars of str are sepc]] wikilink
trim = true;
elseif f.sub(str, -3, -1) == duplicate_char .. '"]' then -- if last three chars of str are sepc"] quoted external link
trim = true;
elseif f.sub(str, -2, -1) == duplicate_char .. "]" then -- if last two chars of str are sepc] external link
trim = true;
elseif f.sub(str, -4, -1) == duplicate_char .. "'']" then -- normal case when |url=something & |title=Title.
trim = true;
end
elseif end_chr == " " then -- if last char of output string is a space
if f.sub(str, -2, -1) == duplicate_char .. " " then -- if last two chars of str are <sepc><space>
str = f.sub(str, 1, -3); -- remove them both
end
end  
if trim then
if value ~= comp then -- value does not equal comp when value contains HTML markup
local dup2 = duplicate_char;
if f.match(dup2, "%A" ) then dup2 = "%" .. dup2; end -- if duplicate_char not a letter then escape it