自定义标签网址的Wordpress htaccess rewriterule

I've done this a dozens times outside of wordpress but for some reason I can't get it to work in wordpress and not sure why. Here's what I'm trying to achieve.

The page http://www.normalpl.com/digital/ has tabbed content, the tabs are books, movies, magazines, etc.

User visits url http://www.normalpl.com/digital/movies/

Display the digital page with the tabbed content, but instead of showing the default 1st tab, the movies tab is shown. The url stays the same in the browser but now wordpress sees http://www.normalpl.com/digital/?tab=movies. So on my digital page I can check what tab the user is trying to view and make that tab visible.

Here's an example of code that's not working on wordpress but I've used before on static sites. Perhaps this wouldn't work on a static site either, but I've done this before using a similar rewrite rule.

RewriteRule ^digital/(movies)[/]?$ http://www.normalpl.com/digital/tab=$1 [L]

Here's the whole htaccess block including wordpress (There are some WPSuperCache rules above this but don't think they have anything to do with my problem).

# BEGIN Digital Media Bucket URLS
<IfModule mod_rewrite.c>
RewriteRule ^[/]?digital/([^/]+)[/]?$ http://www.normalpl.org/digital/?tab=$1 [L,QSA]
</IfModule>
# END Digital Media Bucket URLS

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress