Module:Yesno

return function( arg, default ) arg = type( arg ) == 'string' and mw.ustring.lower( arg ) or arg

if arg == nil then return nil end

if       arg == 'yes' or        arg == 'y' or        arg == 'true' or        tonumber( arg ) ==  1 then return true end

if       arg == 'no' or        arg == 'n' or        arg == 'false' or        arg == '' or        tonumber( arg ) == 0 then return false end

return default end