Responses to MULTISELECT questions are Base-64 encoded to allow the use of spaces which would otherwise be interpreted as separators by the XForms specification.
Every response value must be Base-64 encoded and appropriately padded. Each encoded value must be prefixed with an '@' which serves as a separator while decoding the responses.
It is allowed to use whitespace and/or linebreaks to split long encodings over multiple lines but such splits are only allowed between encoded quadruplets.
<question>@MQ== @Mg== @Mw==</question>
which decodes to the response ('1'; '2'; '3').