Item::offsetGet

public function offsetGet($offset)
{
	$map = $this->getMap();
	$value = null;

	$isImmutable = $this->isImmutable();

	/** @var FieldScalar $field */
	$field = $map[$offset];
	if($field)
	{
		if(!$this->readingFailed)
		{
			// offset is in the cache (values), null-ed or not, but it presents there
			if($this->containsKey($offset))
			{
				return $field->getValue($offset, $this);
			}

			// if the record exists, try to download value from database
			if($this->id)
			{
				$isTabletOrUf = $field->isSourceTablet() || $field->isSourceUserField();
				if($isTabletOrUf)
				{
					if($this->fetchInProgress) // can not go to the endless recursion, sorry...
					{
						return null;
					}
					$this->fetchInProgress = true;
				}

				$tabletLoaded = $this->isTabletLoaded();

				// temporarily disable immutable flag, to allow offsetSet
				if($isImmutable)
				{
					$this->immutable = false;
				}

				// if this is a tablet field, get all tablet (base) data
				if($field->isSourceTablet())
				{
					$this->fetchDataAndCache(!$tabletLoaded, false);
				}
				// the same behaviour is for user field, but get both tablet (base) and user field data
				elseif($field->isSourceUserField())
				{
					$this->fetchDataAndCache(!$tabletLoaded, !$this->setUFLoaded());
				}
				// for other types - get just tablet (base) data
				else
				{
					$this->fetchDataAndCache(!$tabletLoaded, false);
				}

				// restore flag
				if($isImmutable)
				{
					$this->immutable = true;
				}

				if($isTabletOrUf)
				{
					$this->fetchInProgress = false;
				}
			}

			if(!$this->readingFailed) // still no error after download
			{
				$value = $field->getValue($offset, $this);
			}
		}
	}
	else
	{
		// we are beyond the map scope, but this field obviously was set manually
		$value = $this->offsetGetDirect($offset);
	}

	return $value;
}