title: 1and1 .htaccess directives: explanation needed
body: <p>I have no experience with modifying .htaccess file.
  I'm trying to add custom error pages to my website, and I got the following template from the hosting provider (1and1). I know how to add the pages, but I would like to understand line by line what the code is doing.   </p>
  
  <pre><code>RewriteEngine On
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule (.*) /errordocument.html
  ErrorDocument 400 /errordocument.html
  RemoveType x-mapp-php4 .html
  </code></pre>
  
  <p>Thank you in advance for your help!</p>