php: what does . and .. mean in the output of dir->read() -

<?php  $d = dir('css'); echo "handle: " . $d->handle . "<br>"; echo "path: " . $d->path . "<br>";  while (($file = $d->read()) !== false){   echo "filename: " . $file . "<br>"; } $d->close(); ?> 

result:

handle: resource id #4 path: css filename: . filename: .. filename: css filename: img filename: index.html filename: js filename: lightbox 

question:

in result, . , .. mean?

. current directory , .. 1 up. code examples have if-statements skip on em.

here example out of php docs:

http://php.net/manual/en/function.readdir.php#example-2318

even on docs, shows code ignore.