private function parsePlaceholder(\XMLReader $reader, Node $parentNode)
{
$placeholderName = $reader->name;
$innerParser = $this->getInnerParser();
$this->seekReaderToNextTag($reader);
if ($parentNode->hasPlaceholder($placeholderName)) {
$innerParser->setEndTag($placeholderName);
$collection = $innerParser->parse($reader, $this->getStylesheetConstraint());
$placeholder = current($collection->getChildren());
if ($placeholder) {
$parentNode->setPlaceholder($placeholderName, $placeholder);
}
} else {
$element = end($this->tagStack);
throw new ParseException(sprintf('Placeholder "%s" is not supported by "%s" tag.', $placeholderName, $element['tag']));
}
}