apache's mod_rewrite to index.php if 404 unfound/not-found

.htaccess

<IfModule rewrite_module>
#OR<IfModule mod_rewrite.c>
#OR<IfModule mod_rewrite.so>
    # according to apache-documentation, followsymlinks is needed for mod_rewrite
    Options +FollowSymLinks
    # Enable the RewriteEngine
    RewriteEngine On
    # if needed add(/uncomment) the following:
    #RewriteBase /path/to/file/to/be/found/
    # check if the request is not an existing file
    RewriteCond %{SCRIPT_FILENAME} !-f
    # check if the request is not an existing directory
    RewriteCond %{SCRIPT_FILENAME} !-d
    # check if the request is not an existing symlink
    RewriteCond %{SCRIPT_FILENAME} !-s
    # rewrite all requests that passed the conditions to the file index.php
    RewriteRule .* index.php
</IfModule>
# provide fallback if rewrite module is unavailable
#( will by default generate 404-status code to client)
<IfModule !rewrite_module>
#OR<IfModule !mod_rewrite.c>
#OR<IfModule !mod_rewrite.so>
    # if needed the index.php might need to be prefixed with a path.
    ErrorDocument 404 index.php
</IfModule>

# Remember to config the following for the location handled by this .htaccess :
#AllowOverride FileInfo
#or you could do:
#AllowOverride All