Document::setFields

public function setFields(array $fields): Document
{
	foreach($fields as $name => $field)
	{
		// do not let change these fields
		if(
			$name === Template::DOCUMENT_PROVIDER_PLACEHOLDER
			|| $name === Template::MAIN_PROVIDER_PLACEHOLDER
		)
		{
			continue;
		}
		$this->externalFields[$name] = $field;
	}

	return $this;
}