View source for 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 == true or
        arg == 'yes' or
        arg == 'y' or
        arg == 'true' or
        tonumber( arg ) ==  1
    then
        return true
    end

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

    return default
end