'Return the list of HTML option values for a form field value.'

def format_value(self, value):

    if (not isinstance(value, (tuple, list))):
        value = [value]
    values = set()
    for v in value:
        if (not v):
            continue
        if isinstance(v, six.string_types):
            for t in v.split(','):
                values.add(self.option_value(t))
        else:
            for t in v:
                values.add(self.option_value(t))
    return values
