0,1,2,3,4,5,6,7,8,9,10,11,12,"e","f"

0 1 2 3 4 5 e f

$mass=array($a=array($b=array(0,1,2,3,4,5),6,7,8,9,10),11,12,"e","f");

for($i=0;$i<count($mass);$i++){
    for($y=0;$y<count($mass[$i]);$y++){
        for($z=0;$z<count($mass[$i][$y]);$z++){
            echo $mass[$i][$y][$z];
            echo "</br>";
        }
    }
}

<?php
$mass=array(array(array(0,1,2,3,4,5),6,7,8,9,10),11,12,"e","f");

function pr_all($arr)
{
    $out = '';
    foreach ( $arr as $a ) {
        if ( is_array($a) ) {
            $out .= pr_all($a);
        } else {
            $out .= $a . '<br>';
        }
    }
    return $out;
}

echo pr_all($mass);

0<br>1<br>2<br>3<br>4<br>5<br>6<br>7<br>8<br>9<br>10<br>11<br>12<br>e<br>f<br>