public function export_to_xml($question, qformat_xml $format, $extra=null) {
$extraquestionfields = $this->extra_question_fields();
if (!is_array($extraquestionfields)) {
return false;
}
// Omit table name.
array_shift($extraquestionfields);
$expout='';
foreach ($extraquestionfields as $field) {
$exportedvalue = $format->xml_escape($question->options->$field);
$expout .= " <$field>{$exportedvalue}</$field>\n";
}
$extraanswersfields = $this->extra_answer_fields();
if (is_array($extraanswersfields)) {
array_shift($extraanswersfields);
}
foreach ($question->options->answers as $answer) {
$extra = '';
if (is_array($extraanswersfields)) {
foreach ($extraanswersfields as $field) {
$exportedvalue = $format->xml_escape($answer->$field);
$extra .= " <{$field}>{$exportedvalue}</{$field}>\n";
}
}
$expout .= $format->write_answer($answer, $extra);
}
return $expout;
}