Why is enabling the rewrite log in .htaccess not working?

I want to enable rewrite logging so that I can debug a rewrite rule but adding the RewriteLog directives is causing a 500 error.

Version information:

Ubuntu 14.04

Server version: Apache/2.4.12 (Ubuntu)
Server built:   Feb  4 2015 14:22:06

contents of .htaccess

<IfModule mod_rewrite.c>
RewriteEngine On

RewriteLog /var/log/apache2/rewrite.log
RewriteLogLevel 5

RewriteBase /

RewriteRule ^/wordpress/wp-content/(.*)$ /wp-content/$1 [L]

RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

In the error log I see:

/var/www/path.to/wordpress/.htaccess: Invalid command 'RewriteLog', perhaps misspelled or defined by a module not included in the server configuration

In addition to having forgotten that logging cannot be configured in .htaccess files, this also turned out to be an Apache version issue. The RewriteLog directive has been replaced in newer versions and adding the following to the Virtualhost configuration enabled the rewrite log for me:

LogLevel alert rewrite:trace3 (can be increased to trace8)

From the manual:

Those familiar with earlier versions of mod_rewrite will no doubt be looking for the RewriteLog and RewriteLogLevel directives. This functionality has been completely replaced by the new per-module logging configuration mentioned above.

To filter out these messages in the error log you can do something like:

tail -f error_log|fgrep '[rewrite:'

I can't help repeating myself:

Most people who use .htaccess and ask about it on ServerFault should not be using .htaccess in the first place as that is an end-user solution never intended for administrators:

You should avoid using .htaccess files completely if you have access to httpd main server config file. Using .htaccess files slows down your Apache http server. Any directive that you can include in a .htaccess file is better set in a Directory block, as it will have the same effect with better performance.
Source: Apache manual

Apparently most people who publish their configurations appear to be cargo cult programmers keen on copying .htaccess files blindly without understanding the reasons.

Your problem is a prime example: the RewriteLog directive is only valid in the context of a server config or the virtual host...

That means it is not allowed in a .htaccess file!