Why does treating integers as arrays ($int[$index]) not raise any errors in PHP?

I originally thought; it typecasts $int to a string because [] is another way of accessing string positions. Seems plausible that that wouldn't generate an error:

$string 'Hello';
echo $string[0]; // H

However, that's not the case:

$int = 1;
echo $int[0];

Outputs nothing and var_dump($int[0]) returns NULL.

Interestingly, the same behavior is exhibited for bool and float and the operation used is FETCH_DIM_R which is Fetch the value of the element at "index" in "array-value" to store it in "result".

From the manual Arrays:

Note: Array dereferencing a scalar value which is not a string silently yields NULL, i.e. without issuing an error message.

Similar to this phenomenon, where no error is generated. Bugs #68110 and #54556:

$array['a'] = null;
echo $array['a']['non-existent'];

Not surprising that assigning doesn't work:

$int = 1;
$int[0] = 2;

Warning: Cannot use a scalar value as an array

So PHP is actually attempting to access the int, bool, float as an array but not generating an error. This is from at least version 4.3.0 to 7.2.2.