Multisite is the most talked about new feature in WordPress 3.0 – the WordPress team has folded the functionality of WordPress Multiuser into the main WordPress project. So how do you use it?

This tutorial assumes your are comfortable using FTP clients such as Filezilla and doing basic edits of WordPress files.

1. Download WordPress 3.0 release candidate. You can find it here.

2. Edit wp-config in your favorite text editor and add the following line:

define(‘WP_ALLOW_MULTISITE’, true);

(I’d suggest adding it just above the line “// ** MySQL settings – You can get this info from your web host ** //”)

3. Install WordPress normally

NOTE: If you’ve already installed WordPress 3.0, just edit wp-config and add that line of code, there’s no need to re-install.

4. Under Tools on the sidebar, you’ll now have an “Network” option. Click it.

5. Here you’ll setup your “Network” – a Network is all the blogs or sites you’ll have under your WordPress install (if you’re migrating back to WordPress from WordPress Multiuser this might be confusing. In WordPress Multiuser the term for network was “site” and the term for site was “blog.” Explanation here).

If your host supports it, you’ll have the option here to choose between subdomains and subdirectories.

Example of a subdomain: site1.yourdomain.com
Example of a subdirectory: yourdomain.com/site1

Fill out your Network Title and Admin E-mail Address and press install.

6. You’ll be greeted with your next list of steps: creating a blogs.dir directory, editing wp-config.php, and .htaccess. WP recommends, as do I, backing up wp-config.php and .htaccess files before proceeding.

After completing the steps, you’ll need to log back into WordPress.

7. On your next login, you’ll notice a new menu: “Super Admin.”

8. Click “Sites” under this option to create a new site. Fill out the forms accordingly.

9. After creating a new site, click Users. You’ll see a new user was created for the new site.

10. You can control all sites on your network through the Super Admin menu, but for right now you might find it easier to administer individual sites through their own admin menus. You can access them as you would a normal wordpress site. In the example above, it would be: http://mydomain.net/malta/wp-admin

I did! I was working on a project recently that needed a plugin. The only problem was that the plugin was inserting some unnecessary cruft into the header of my theme. So, I figured I’d just use the remove_filter function WordPress provides… right?

Hold on a second! It’s not working!? But I put in the function name just how the codex explains it:

remove_filter('wp_head', 'the_crufty_function');

Why would it not work? Time to do some troubleshooting… So, I opened up the main plugin PHP file in my code editor and began to look around. What’s this? It’s a class! Hmm… But why should that make a difference?

It seems that WordPress requires a special reference to the function if it is defined inside a class. If you, the reader, are at all familiar with PHP classes then you probably know that you can usually access a class’s functions like this:

$the_class_initiator_variable->some_function();

So, lets give that a try:

remove_filter('wp_head', $the_crufty_class->the_crufty_function);

Still nothing… Oh boy… What do I do now? I guess we’ll try some Googling…

…Hmm…

…Not finding much…

Well… after much searching and trying different things I finally came upon this:

remove_filter('wp_head', array(&$the_crufty_class, 'the_crufty_function'));

It works! Wonderful!

You take the class initiator variable and the name of the function and put it in an array. Simple as that!

Note: No, that ampersand is not a typo! It sets up a reference to the original variable instead of copying it’s value. You’d be surprised how many people don’t know what the ampersand does in PHP. I didn’t know for the longest time.

Also, because the remove_filter and remove_action functions are so similar this method applies to both.

There you have it! Just a quick little tip regarding an issue that doesn’t seem to be very well documented. I’m sure some of the experts out there already know of this but, I didn’t. I’m willing to assume there are some people out there like me who are racking their brains over this very issue.

Hope it helps!

If you want to create a site similar to twitter, Cats Who Code has a excellent step by step tutorial that will help you create a private twitter site using WordPress.

BTW if you are on twitter, don’t forget to follow us @weblogtooltips.

The book, written for anyone who wishes to author WordPress plugins, consists of eight chapters, six of which are dealing with development of actual plugins from scratch.

Here’s what you can learn:

• Get to know the WordPress code base, WordPress’s plug-in architecture, and the plug-in application programming interface (API) and learn how to hack it
• Master the WordPress database and the API – access and manipulate data, handle user roles and permissions, posts, and so on
• Hook into the rest of WordPress using actions and filters
• Change the way your WordPress backend looks by customizing menus, submenus, and the plug-in admin panel
• Integrate AJAX and jQuery into your plug-ins to dynamically generate content
• Hook directly to WordPress edit pages and use AJAX to generate fast searches
• Integrate your plug-in with WordPress panels and the tinyMCE editor
• Access and work with third-party APIs like Flickr
• Implement localization support for users of other languages
• Maintain and manage your plug-in using SVN and publish it to the WordPress Plugin Repository
• Handle security issues and make your plug-ins safer to use

The book retails for $39.99 for the hard copy and $31.99 for the eBook. You can order the same from Packt Publishing or Amazon.

This tutorial makes use of Custom Fields in WordPress using the various functions that help manage Custom Fields (I keep typing customer), and is a shining example of how useful and flexible Custom Fields can be in developing a full CMS with WordPress.

Since the final code is included in the tutorial, if you were to put together a Custom Write Panel for your blog with the help of the tutorial, what would you use it for? I would love to use it to add updates to posts, which would then be displayed with some extra styling and markup to denote the change in status of the item in the post.