WordPress.org

Author: Dan Phiffer

Strict Permalinks does two things:

1. Restricts the post_name portion of the permalink to alphanumerics and hyphens
2. Disables permalink editing once a post is published

Like me, you may have been under the impression that post "slugs" are already restricted to alphanumerics and hyphens. In the current WordPress 2.8.5, a title that includes typographically-correct punctuation (a.k.a. "smartquotes") will result in URL-encoded characters in the post_name field. Many browsers handle this oddity seamlessly, however this may cause difficulties when integrating with systems expecting a more limited URL syntax.