What does the line $fla[$data[feld1]][$data[feld2]] = $data do in the PHP code provided?

The line $fla[$data[feld1]][$data[feld2]] = $data is attempting to assign the value of $data to a multi-dimensional array $fla at the indices specified by $data[feld1] and $data[feld2]. However, since "feld1" and "feld2" are not enclosed in quotes, PHP will interpret them as constants rather than keys in the $data array, resulting in an error. To fix this, the keys should be enclosed in quotes to correctly access the values in the $data array.

$fla[$data['feld1']][$data['feld2']] = $data;