How to make redirect to 404 or root page when user types query to not existing page and SSI include gets error?
Or how to check if HTML-document exist on server and if doesn't then also make redirect?
If user types domain.tld?anyquerystring
on my site then it includes anyquerystring.html
HTML-page by SSI.
If user types query of not existing page like domain.tld?blahblahblah
then it gives the [an error occurred while processing this directive]
in the place of SSI include.
You can configure error message in SSI. The answer is
<!--#config errmsg="Put here your error message, HTML or other code" -->