Standard "custom" Error Page For CSP Web Application

Hi folks!

It's not an innovation, but often I saw not a very informative Error page for CSP apps and got it for myself. Something like that:

Turned out that it is relatively easy to make the same page return meaningful error messages. Just add %CSP.Error.cls as a Custom error handling class here:

And the same page will start showing meaningful errors, like in a screenshot below:

Credit goes to @Sean Connelly