code: public function offsetExists($offset)
      {
          if ($offset === false) {
              return $this->falseValueIsSet;
          }
          if ($offset === true) {
              return $this->trueValueIsSet;
          }
          if (is_int($offset) || is_string($offset)) {
              return array_key_exists($offset, $this->standardStore);
          }
          if (is_float($offset)) {
              return array_key_exists((string) $offset, $this->floatStore);
          }
          if (is_object($offset)) {
              return $this->objectStore->offsetExists($offset);
          }
          if (is_array($offset)) {
              foreach ($this->arrayKeys as $index => $entry) {
                  if ($entry === $offset) {
                      $this->lastArrayKey   = $offset;
                      $this->lastArrayValue = $this->arrayValues[$index];
  
                      return true;
                  }
              }
          }
          if ($offset === null) {
              return $this->nullValueIsSet;
          }
  
          return false;
      }
docs: Whether a offset exists
  
  @link http://php.net/manual/en/arrayaccess.offsetexists.php
  
  @param mixed $offset <p>
  An offset to check for.
  </p>
  
  @return bool true on success or false on failure.
  </p>
  <p>
  The return value will be casted to boolean if non-boolean was returned.