Html::getPlaceholders

public function getPlaceholders()
{
	$names = static::matchFieldNames($this->content);

	$variableAttributes = [
		'condition', 'from', 'to',
	];
	$commandNodes = $this->htmlDocument->querySelectorAll('command');
	foreach($commandNodes as $nextCommand)
	{
		$nodeAttributes = static::getNodeAttributes($nextCommand);
		foreach($variableAttributes as $attribute)
		{
			if($nodeAttributes[$attribute])
			{
				$names[] = $nodeAttributes[$attribute];
			}
		}
	}

	return $names;
}