Why does mod_rewrite ignore my [L] flag? - apache

Question

This is my .htaccess file. It should deliver static files from assets folder if the url matches them. Otherwise, everything should be redirected to index.php.
Note that the url doesn't contain assets as segemnt here. So example.com/css/style.css directs to assets/css/style.css.
RewriteEngine on
# disable directory browsing
Options -Indexes
# static assets
RewriteCond %{DOCUMENT_ROOT}/assets/$1 -f
RewriteRule ^(.*)$ assets/$1 [L]
# other requests to index.php
RewriteRule !^asset/ index.php [L]
Unfortunately, urls like example.com/assets/css/style.css also deliver the file, since for that url none of my rules applies and Apache's default behavior is applied which delivers the file.
So I tried changing the last line to this. I thought that this would work since the [L] flag in the rule above should stop execution for asset urls and deliver them.
RewriteRule ^(.*)$ index.php [L]
Instead, not all requests are redirected to index.php, even static assets like example.com/css/style.css. Why does the flag not stop execution of rewrite rules and who to fix my problem then?

Answer 1

I found the solution on the pages of the official documentation.
If you are using RewriteRule in either .htaccess files or in
sections, it is important to have some understanding of
how the rules are processed. The simplified form of this is that once
the rules have been processed, the rewritten request is handed back to
the URL parsing engine to do what it may with it. It is possible that
as the rewritten request is handled, the .htaccess file or
section may be encountered again, and thus the ruleset may be run
again from the start. Most commonly this will happen if one of the
rules causes a redirect - either internal or external - causing the
request process to start over.
It is therefore important, if you are using RewriteRule directives in
one of these contexts, that you take explicit steps to avoid rules
looping, and not count solely on the [L] flag to terminate execution
of a series of rules, as shown below.
An alternative flag, [END], can be used to terminate not only the
current round of rewrite processing but prevent any subsequent rewrite
processing from occurring in per-directory (htaccess) context. This
does not apply to new requests resulting from external redirects.
To fix my problem, I changed to [L] flags to [END].
RewriteEngine on
# disable directory browsing
Options -Indexes
# static assets
RewriteCond %{DOCUMENT_ROOT}/assets/$1 -f
RewriteRule ^(.*)$ assets/$1 [END]
# other requests to index.php
RewriteRule !^asset/ index.php [END]