system/HTTP/ContentSecurityPolicy.php
public function addSandbox($flags, ?bool $explicitReporting = null)
	{
		$this->addOption($flags, 'sandbox', $explicitReporting ?? $this->reportOnly);
		return $this;
	}
public function addSandbox($flags, ?bool $explicitReporting = null)
	{
		$this->addOption($flags, 'sandbox', $explicitReporting ?? $this->reportOnly);
		return $this;
	}
specifies an HTML sandbox policy that the user agent applies to
the protected resource.

@see http://www.w3.org/TR/CSP/#directive-sandbox

@param string|array $flags             An array of sandbox flags that can be added to the directive.
@param boolean|null $explicitReporting

@return $this