Module:Check for unknown parameters/sandbox

 -- This module may be used to compare the arguments passed to the parent
 -- with a list of arguments, returning a specified result if an argument is
 -- not on the list
 local p = {}

 local function trim(s)
	return s:match('^%s*(.-)%s*$')
 end

 local function isnotempty(s)
	return s and s:match('%S')
 end

 local function clean(text)
	-- Return text cleaned for display and truncated if too long.
	-- Strip markers are replaced with dummy text representing the original wikitext.
	local truncated
	local function truncate(text)
		if truncated then
			return ''
		end
		if mw.ustring.len(text) > 25 then
			truncated = true
			text = mw.ustring.sub(text, 1, 25) .. '...'
		end
		return mw.text.nowiki(text)
	end
	local parts = {}
	local pos
	for before, tag, remainder in text:gmatch('([^127円]*)127円[^127円]*%-(%l+)%-[^127円]*127円()') do
		pos = remainder
		table.insert(parts, truncate(before) .. '<' .. tag .. '>...</' .. tag .. '>')
	end
	table.insert(parts, truncate(text:sub(pos or 1)))
	return table.concat(parts)
 end

 local function get_values(args, pargs)
	-- create the list of known args, regular expressions, and the return string
	local knownargs = {}
	local regexps = {}
	for k, v in pairs(args) do
		if type(k) == 'number' then
			v = trim(v)
			knownargs[v] = 1
		elseif k:find('^regexp[1-9][0-9]*$') then
			table.insert(regexps, '^' .. v .. '$')
		end
	end
	-- loop over the parent args, and make sure they are on the list
	local ignoreblank = isnotempty(args['ignoreblank'])
	local showblankpos = isnotempty(args['showblankpositional'])
	local values = {}
	for k, v in pairs(pargs) do
		if type(k) == 'string' and knownargs[k] == nil then
			local knownflag = false
			for _, regexp in ipairs(regexps) do
				if mw.ustring.match(k, regexp) then
					knownflag = true
					break
				end
			end
			if not knownflag and ( not ignoreblank or isnotempty(v) ) then
				table.insert(values, clean(k))
			end
		elseif type(k) == 'number' and knownargs[tostring(k)] == nil then
			local knownflag = false
			for _, regexp in ipairs(regexps) do
				if mw.ustring.match(tostring(k), regexp) then
					knownflag = true
					break
				end
			end
			if not knownflag and ( showblankpos or isnotempty(v) ) then
				table.insert(values, k .. ' = ' .. clean(v))
			end
		end
	end
	return values
 end

 function p._check(args, pargs)
	if type(args) ~= "table" or type(pargs) ~= "table" then
		-- TODO: error handling
		return
	end

	local values = get_values(args, pargs)

	-- add results to the output tables
	local previews = {}
	local categories = {}
	local unknown_category = args['unknown']
	local preview_text = args['preview'] or 'Found _VALUE_, '
	if #values > 0 then
		preview_text = require('Module:If preview')._warning({preview_text})

		for _, v in pairs(values) do
			-- Fix odd bug for | = which gets stripped to the empty string and
			-- breaks category links
			if v == '' then v = ' ' end

			-- avoid error with v = 'example%2' ("invalid capture index")
			local category = unknown_category:gsub('_VALUE_', {_VALUE_ = v})
			local preview = preview_text:gsub('_VALUE_', {_VALUE_ = v})
			table.insert(categories, category)
			table.insert(previews, preview)
		end
	end

	return table.concat(previews) .. "\n" .. table.concat(categories)
 end

 function p.check(frame)
	local args = frame.args
	local pargs = frame:getParent().args
	return p._check(args, pargs)
 end

 return p