system/API/ResponseTrait.php
protected function format($data = null)
	{
		// If the data is a string, there's not much we can do to it...
		if (is_string($data))
		{
			// The content type should be text/... and not application/...
			$contentType = $this->response->getHeaderLine('Content-Type');
			$contentType = str_replace('application/json', 'text/html', $contentType);
			$contentType = str_replace('application/', 'text/', $contentType);
			$this->response->setContentType($contentType);

			return $data;
		}

		// Determine correct response type through content negotiation
		$config = new Format();
		$format = $this->request->negotiate('media', $config->supportedResponseFormats, false);

		$this->response->setContentType($format);

		// if we don't have a formatter, make one
		if (! isset($this->formatter))
		{
			// if no formatter, use the default
			$this->formatter = $config->getFormatter($format);
		}

		if ($format !== 'application/json')
		{
			// Recursively convert objects into associative arrays
			// Conversion not required for JSONFormatter
			$data = json_decode(json_encode($data), true);
		}

		return $this->formatter->format($data);
	}
protected function format($data = null)
	{
		// If the data is a string, there's not much we can do to it...
		if (is_string($data))
		{
			// The content type should be text/... and not application/...
			$contentType = $this->response->getHeaderLine('Content-Type');
			$contentType = str_replace('application/json', 'text/html', $contentType);
			$contentType = str_replace('application/', 'text/', $contentType);
			$this->response->setContentType($contentType);

			return $data;
		}

		// Determine correct response type through content negotiation
		$config = new Format();
		$format = $this->request->negotiate('media', $config->supportedResponseFormats, false);

		$this->response->setContentType($format);

		// if we don't have a formatter, make one
		if (! isset($this->formatter))
		{
			// if no formatter, use the default
			$this->formatter = $config->getFormatter($format);
		}

		if ($format !== 'application/json')
		{
			// Recursively convert objects into associative arrays
			// Conversion not required for JSONFormatter
			$data = json_decode(json_encode($data), true);
		}

		return $this->formatter->format($data);
	}
Handles formatting a response. Currently makes some heavy assumptions
and needs updating! :)

@param string|array|null $data

@return string|null