WordPress.org

Install

1. Copy sitewide-tags.php into wp-content/mu-plugins/
2. Login as a site administrator and go to Site Admin, Options. A number of extra options are created:
   1. "Tags blog" defaults to "tags" but can be anything. This is the blog where your sitewide posts will live. It will be created if it doesn't exist.
   2. "Max posts" defaults to 5000. Older posts will be deleted if this threshold is broken.
   3. "Privacy" defaults to public, pages can be indexed by search engines.