public function timestampedFileName( $extension, $fullpath = true ) {
		$book_title = ( get_bloginfo( 'name' ) ) ? get_bloginfo( 'name' ) : __( 'book', 'pressbooks' );
		$book_title_slug = sanitize_file_name( $book_title );
		$book_title_slug = str_replace( [ '+' ], '', $book_title_slug ); // Remove symbols which confuse Apache (Ie. form urlencoded spaces)
		$book_title_slug = sanitize_file_name( $book_title_slug ); // str_replace() may inadvertently create a new bad filename, sanitize again for good measure.

		if ( $fullpath ) {
			$path = static::getCoversFolder();
		} else {
			$path = '';
		}

		$filename = $path . $book_title_slug . '-cover-' . time() . '.' . ltrim( $extension, '.' );

		return $filename;
	}