local function display_names_select (global_display_names, local_display_names, param_name, number_of_names, test)
if global_display_names and utilities.is_set (local_display_names) then -- when both
if 'etal' == local_display_names:lower:gsub("[ '%.]", '') then -- the :gsub portion makes 'etal' from a variety of 'et al.' spellings and stylings
number_of_names = tonumber (number_of_names); -- convert these to numbers for comparison
local global_display_names_num = tonumber (global_display_names); -- <global_display_names> not set when parameter value is not digits  
if number_of_names > global_display_names_num then -- template has more names than global config allows to be displayed?
utilities.set_message ('maint_overridden_setting'); -- set a maint message because global is overriding local |display-<namelist>=etal
return global_display_names, 'cs1 config'; -- return global with spoof parameter name (for get_display_names)
else
return local_display_names, param_name; -- return local because fewer names so let <local_display_names> control
end
end
-- here when <global_display_names> and <local_display_names> both numbers; <global_display_names> controls
utilities.set_message ('maint_overridden_setting'); -- set a maint message
return global_display_names, 'cs1 config'; -- return global with spoof parameter name (for get_display_names)
end
-- here when only one of <global_display_names> or <local_display_names> set
if global_display_names then
return global_display_names, 'cs1 config'; -- return global with spoof parameter name (for get_display_names)
else
return local_display_names, param_name; -- return local
end
end  
----------------------------< C I T A T I O N 0 >------------------------------------------------------------  
This is the main function doing the majority of the citation formatting.  
local function citation0( config, args )
---
Load Input Parameters
The argument_wrapper facilitates the mapping of multiple aliases to single internal variable.  
local A = argument_wrapper ( args );
local i  
-- Pick out the relevant fields from the arguments. Different citation templates
-- define different field names for the same underlying things.  
local author_etal;
local a = {}; -- authors list from |lastn= / |firstn= pairs or |vauthors=
local Authors;
local NameListStyle;
if cfg.global_cs1_config_t['NameListStyle'] then -- global setting in overrides local |name-list-style= parameter value; nil when empty or assigned value invalid
NameListStyle = is_valid_parameter_value (cfg.global_cs1_config_t['NameListStyle'], 'cs1 config: name-list-style', cfg.keywords_lists['name-list-style'], ''); -- error messaging 'param' here is a hoax
else
NameListStyle = is_valid_parameter_value (A['NameListStyle'], A:ORIGIN('NameListStyle'), cfg.keywords_lists['name-list-style'], '');
end  
if cfg.global_cs1_config_t['NameListStyle'] and utilities.is_set (A['NameListStyle']) then -- when template has |name-list-style=<something> which global setting has overridden
utilities.set_message ('maint_overridden_setting'); -- set a maint message
end  
local Collaboration = A['Collaboration'];  
do -- to limit scope of selected
local selected = select_author_editor_source (A['Vauthors'], A['Authors'], args, 'AuthorList');
if 1 == selected then
a, author_etal = extract_names (args, 'AuthorList'); -- fetch author list from |authorn= / |lastn= / |firstn=, |author-linkn=, and |author-maskn=
elseif 2 == selected then
NameList; -- override whatever |name-list-style= might be
a, author_etal = parse_vauthors_veditors (args, A['Vauthors'], 'AuthorList'); -- fetch author list from |vauthors=, |author-linkn=, and |author-maskn=
elseif 3 == selected then
Authors = A['Authors']; -- use content of |people= or |credits=; |authors= is deprecated; TODO: constrain |people= and |credits= to cite av media, episode, serial?
end
if utilities.is_set (Collaboration) then
author_etal = true; -- so that |display-authors=etal not required
end
end  
local editor_etal;
local e = {}; -- editors list from |editor-lastn= / |editor-firstn= pairs or |veditors=  
do -- to limit scope of selected
local selected = select_author_editor_source (A['Veditors'], nil, args, 'EditorList'); -- support for |editors= withdrawn
if 1 == selected then
e, editor_etal = extract_names (args, 'EditorList'); -- fetch editor list from |editorn= / |editor-lastn= / |editor-firstn=, |editor-linkn=, and |editor-maskn=
elseif 2 == selected then
NameList; -- override whatever |name-list-style= might be
e, editor_etal = parse_vauthors_veditors (args, args.veditors, 'EditorList'); -- fetch editor list from |veditors=, |editor-linkn=, and |editor-maskn=
end
end  
local Chapter = A['Chapter']; -- done here so that we have access to |contribution= from |chapter= aliases
local Chapter_origin = A:ORIGIN ('Chapter');
local Contribution; -- because contribution is required for contributor(s)
if 'contribution' == Chapter_origin then
Contribution = Chapter; -- get the name of the contribution
end
local c = {}; -- contributors list from |contributor-lastn= / contributor-firstn= pairs  
if utilities.in_array (config.CitationClass, {"book", "citation"}) and not utilities.is_set (A['Periodical']) then -- |contributor= and |contribution= only supported in book cites
c = extract_names (args, 'ContributorList'); -- fetch contributor list from |contributorn= / |contributor-lastn=, -firstn=, -linkn=, -maskn=  
if 0 < #c then
if not utilities.is_set (Contribution) then -- |contributor= requires |contribution=
utilities.set_message ('err_contributor_missing_required_param', 'contribution'); -- add missing contribution error message
c = {}; -- blank the contributors' table; it is used as a flag later
end
if 0 == #a then -- |contributor= requires |author=
utilities.set_message ('err_contributor_missing_required_param', 'author'); -- add missing author error message
c = {}; -- blank the contributors' table; it is used as a flag later
end
end
else -- if not a book cite
if utilities.select_one (args, cfg.aliases['ContributorList-Last'], 'err_redundant_parameters', 1 ) then -- are there contributor name list parameters?
utilities.set_message ('err_contributor_ignored'); -- add contributor ignored error message
end
Contribution = nil; -- unset
end  
local Title = A['Title'];
local TitleLink = A['TitleLink'];  
local auto_select = ''; -- default is auto
local accept_link;
TitleLink, accept_link = utilities.has_accept_as_written (TitleLink, true); -- test for accept-this-as-written markup
if (not accept_link) and utilities.in_array (TitleLink, {'', 'pmc', 'doi'}) then -- check for special keywords
auto_select = TitleLink; -- remember selection for later
TitleLink = ''; -- treat as if |title-link= would have been empty
end  
TitleLink = link_title_ok (TitleLink, A:ORIGIN ('TitleLink'), Title, 'title'); -- check for wiki-markup in |title-link= or wiki-markup in |title= when |title-link= is set  
local Section = ''; -- only; preset to empty string for concatenation if not used
if 'map' == config.CitationClass and 'section' == Chapter_origin then
Section = A['Chapter']; -- get |section= from |chapter= alias list; |chapter= and the other aliases not supported in
Chapter = ''; -- unset for now; will be reset later from |map= if present
end  
local Periodical = A['Periodical'];
local Periodical_origin = A:ORIGIN('Periodical');
local ScriptPeriodical = A['ScriptPeriodical'];
local ScriptPeriodical_origin = A:ORIGIN('ScriptPeriodical');
local TransPeriodical = A['TransPeriodical'];
local TransPeriodical_origin = A:ORIGIN ('TransPeriodical');  
if (utilities.in_array (config.CitationClass, {'book', 'encyclopaedia'}) and (utilities.is_set (Periodical) or utilities.is_set (ScriptPeriodical) or utilities.is_set (TransPeriodical))) then
local param;
if utilities.is_set (Periodical) then -- get a parameter name from one of these periodical related meta-parameters
Periodical = ''; -- unset because not valid or parameters