system/HTTP/UserAgent.php
public function isBrowser(string $key = null): bool
	{
		if (! $this->isBrowser)
		{
			return false;
		}

		// No need to be specific, it's a browser
		if ($key === null)
		{
			return true;
		}

		// Check for a specific browser
		return (isset($this->config->browsers[$key]) && $this->browser === $this->config->browsers[$key]);
	}
public function isBrowser(string $key = null): bool
	{
		if (! $this->isBrowser)
		{
			return false;
		}

		// No need to be specific, it's a browser
		if ($key === null)
		{
			return true;
		}

		// Check for a specific browser
		return (isset($this->config->browsers[$key]) && $this->browser === $this->config->browsers[$key]);
	}
Is Browser

@param string $key

@return boolean