When there is an uncaught exception, Drupal 8 displays a simple dump of the exception.

I find that the page is served as 'Content-Type' = 'text/plain', yet it contains HTML:

It looks better to me when I change the code to serve as 'text/html':

I already found the code to change - it's in FinalExceptionSubscriber.php, which outputs

• </br></br>
• SafeMarkup::format(...) which is documented as

Formats a string for HTML display by replacing variable placeholders.

My question is:

1. Does anyone know a reason why the error page is text/plain given that it contains HTML.
2. Shall I raise an issue and patch?