.htaccess: RewriteRule: bad flag delimiters

Question

I added

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} /article/
RewriteRule ! ^article/\d+ redirect.php [L]

to .htaccess and got a .htaccess: RewriteRule: bad flag delimiters message. Reviewed the related questions here but they didn't help.

Answer 1

Compare

RewriteRule ! ^article/\d+ redirect.php [L]
RewriteRule !^article/\d+ redirect.php [L]

Yes, the second works. You can't have a space between the ! and the pattern. AFAICS this is not mentioned in the Apache docs.