code: function render_stack_trace(error, { markup_settings, log })
  {
  	// Supports custom `html` for an error
  	if (error.html)
  	{
  		return { response_status: error.status, response_body: error.html }
  	}
  
  	// Handle `superagent` errors
  	// https://github.com/visionmedia/superagent/blob/29ca1fc938b974c6623d9040a044e39dfb272fed/lib/node/response.js#L106
  	if (error.response && typeof error.status === 'number')
  	{
  		// If the `superagent` http request returned an HTML response 
  		// (possibly an error stack trace),
  		// then just output that stack trace.
  		if (error.response.headers['content-type']
  			&& error.response.headers['content-type'].split(';')[0].trim() === 'text/html')
  		{
  			return { response_status: error.status, response_body: error.message }
  		}
  	}
  
  	// If this error has a stack trace then it can be shown
  
  	let stack_trace
  
  	if (error.stack)
  	{
  		stack_trace = error.stack
  	}
  	// `superagent` errors have the `original` property 
  	// for storing the initial error
  	else if (error.original && error.original.stack)
  	{
  		stack_trace = error.original.stack
  	}
  
  	// If this error doesn't have a stack trace - do nothing
  	if (!stack_trace)
  	{
  		return {}
  	}
  
  	// Render the error's stack trace as HTML markup
  	try
  	{
  		return { response_body: html_stack_trace({ stack: stack_trace }, markup_settings) }
  	}
  	catch (error)
  	{
  		log.error(error)
  
  		// If error stack trace couldn't be rendered as HTML markup,
  		// then just output it as plain text.
  		return { response_body: error.stack }
  	}
  }
docs: Renders the stack trace of an error as HTML markup