Module:Correct title categories

local p = {}
function p.main(frame)
	return p._main(frame.args[1])
end
function p._main(title)
	title = title:gsub("'","")
	-- Add a trailing "a" to distinguish empty from no fragment
	local titleObj = mw.title.new(title.."a")
	if not titleObj or title == "/." then
		return "[[Category:Restricted titles (illegal characters)]]"
	elseif #titleObj.fragment > 0 then
		if #titleObj.text > 0 then
			return "[[Category:Restricted titles (number sign)]]"
		else
			return "[[Category:Restricted titles (leading number sign)]]"
		end
	elseif #titleObj.interwiki > 0 then
		return "[[Category:Restricted titles (interwiki prefix)]]"
	elseif not titleObj.isContentPage then
		return "[[Category:Restricted titles (namespace)]]"
	else
		return "[[Category:Pages using technically valid titles in correct title hatnotes]]"
	end
end
return p