It should be noted that offsetExists behaves like "offsetIsSet" rather than "offsetIsValid":<?php$arr = new SplFixedArray(3);var_dump($arr->offsetExists(1)); // false$arr[1] = 42; // $arr->offsetSet(1, 42);var_dump($arr->offsetExists(1)); // true$arr[1] = null; // $arr->offsetSet(1, null);var_dump($arr->offsetExists(1)); // trueunset($arr[1]); // $arr->offsetUnset(1);var_dump($arr->offsetExists(1)); // falsevar_dump($arr);/*object(SplFixedArray)[1] null null null*/?>