htaccess重写规则仅适用于数字通配符

Question

My htaccess rewrite rule is working as desired if I use digits in the wildcard, but if I use letters, I get a 404. I am attempting to rewrite the URL, not redirect.

It seems like I should be able to replace ([0-9]+) with ([a-z]+) to get letters to work, or replace with ([.*]+) to get anything to work, however - I get 404's when I try anything to expect ([0-9]+).

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

# END WordPress
<IfModule mod_rewrite.c>
    RewriteEngine on
   RewriteRule ^([0-9]+)\/?$ mydirectory/index.php?param=$1 [NC]
</IfModule>

I feel like I should be able to replace this line:

RewriteRule ^([0-9]+)\/?$ mydirectory/index.php?param=$1 [NC]

with this line:

RewriteRule ^([a-z]+)\/?$ mydirectory/index.php?param=$1 [NC]

However, this doesn't work.

The desired URL is http://mydomainname.com/mydirectory/myparameter/