src/ArrayObject.php
public function offsetExists($offset)
    {
        return ArrayHelper::isIndexed($this->data) && count($this->data) > $offset;
    }
public function offsetExists($offset)
    {
        return ArrayHelper::isIndexed($this->data) && count($this->data) > $offset;
    }
(PHP 5 &gt;= 5.0.0)<br/>
Whether a offset exists
@link http://php.net/manual/en/arrayaccess.offsetexists.php

@param mixed $offset <p>
An offset to check for.
</p>

@return boolean true on success or false on failure.
</p>
<p>
The return value will be casted to boolean if non-boolean was returned.