protected function getProperties( $html_file ) {

		$html = \Pressbooks\Utility\get_contents( $html_file );
		$properties = [];

		if ( empty( $html ) ) {
			throw new \Exception( 'File contents empty for getProperties' );
		}

		if ( $this->isMathML( $html ) ) {
			$properties['mathml'] = 1;
		}

		if ( $this->isScripted( $html ) ) {
			$properties['scripted'] = 1;
		}

		// TODO: Check for remote resources

		return $properties;
	}