protected function pbCheck( array $xml ) {

		$pt = 0;
		$ch = 0;
		$fm = 0;
		$bm = 0;
		$meta = 0;

		foreach ( $xml['posts'] as $p ) {

			if ( 'part' === $p['post_type'] ) {
				$pt = 1;
			} elseif ( 'chapter' === $p['post_type'] ) {
				$ch = 1;
			} elseif ( 'front-matter' === $p['post_type'] ) {
				$fm = 1;
			} elseif ( 'back-matter' === $p['post_type'] ) {
				$bm = 1;
			} elseif ( 'metadata' === $p['post_type'] ) {
				$meta = 1;
			}

			if ( $pt + $ch + $fm + $bm + $meta >= 2 ) {
				$this->isPbWxr = true;
				break;
			}
		}

	}