private function content($content, callable $export, callable $import, callable $insert)
{
if (isset($content)) {
$callback = Constraints::isCallable($content, FALSE, TRUE);
if ($callback) {
foreach ($this->_nodes as $index => $node) {
$contentString = $callback($node, $index, $export($node));
$insert($node, $import($contentString));
}
} else {
$fragment = $import($content);
foreach ($this->_nodes as $node) {
$insert($node, $fragment);
}
}
return $this;
} elseif (isset($this->_nodes[0])) {
return $export($this->_nodes[0]);
}
return '';
}