WordPress 2.3 has built-in support for some common and useful tag and category queries. A public query variable named “tag” allows retrieving all posts associated with one or more tags. Here are some examples.

• tag=wordpress-23 fetches all posts on this blog with the “WordPress 2.3″ tag.
• tag=wordpress-23,wordpress-24 fetches posts with either the “WordPress 2.3″ or the “WordPress 2.4″ tag.
• tag=wordpress-23+wordpress-24 fetches posts with both the “WordPress 2.3″ and the “WordPress 2.4″ tag.

There are also a number of private query variables that plugins can use to perform union and intersection queries for categories and tags. Plugins can insert these queries into the global query by hooking onto the ‘parse_request’ action and calling $wp->set_query_var() from their handler.

• category__in - Accepts an array of category IDs. Fetches posts in any one of the specified categories.
• category__not_in - Accepts an array of category IDs. Fetches posts that are not in any of the specified categories.
• category__and - Accepts an array of category IDs. Fetches posts that are in all of the specified categories.
• tag__in - Accepts an array of tag IDs. Fetches posts having any one of the specified tags.
• tag__not_in - Accepts an array of tag IDs. Fetches posts that do not have any of the specified tags.
• tag__and - Accepts an array of tag IDs. Fetches posts that have all of the specified tags.
• tag_slug__in - Accepts an array of tag slugs. Fetches posts having any one of the specified tags.
• tag_slug__and - Accepts an array of tag slugs. Fetches posts that have all of the specified tags.

WordPress 2.3 arrived a couple days ago. Reception has been very positive, and most people seem pleased with it.  As expected, plugin compatibility due to the schema changes caused some grief. Two very popular plugins that need to be upgraded when moving to 2.3 are Google Sitemaps and Extended Live Archives. If you have one of those plugins, please be sure to upgrade to the latest version.

This being a major release with lots of changes, some little bugs have popped up. We’re fixing them as they come in and targeting them for an eventual 2.3.1 release. A release date for 2.3.1 has not yet been set, but we typically follow a major release with a “dot one” bug fix release within a month or so. You can watch the activity on the 2.3.1 milestone to see what bugs are being reported and fixed. If you have any problems with 2.3, please report them so we can get them fixed.

With 2.3 done, we’ve started work on 2.4. This is the exciting phase of development where we get to work on new features, and 2.4 promises to have lots of new features. Whereas 2.3 had more of an infrastructure focus, 2.4 looks like it will focus on UI and user experience. I’m excited about the features being pitched for 2.4. There’ll be more on that as the feature list is finalized and the designs and code start to flow. For now I’ll leave you with the tease of cool things to come.

Aaron offers a good overview of WordPress 2.3 in his 10 Things You Need to Know About WordPress 2.3 writeup.

The new tagging feature in WordPress 2.3 was kept purposefully simple. We focused on providing infrastructure that cool tagging plugins could use. As noted by Weblog Tools Collection, there are already two tagging plugins that work with 2.3. Advanced Tag Entry and Click Tags are from regular WordPress contributors Jennifer Hodgdon and Andy Staines. Check these out if you want something a little fancier than what is built into 2.3.

Watching to see how plugin authors enhance tagging will be fun. Some of the most popular features added by plugins will likely wind up in 2.4. I like releasing something simple, letting plugin authors innovate and extend, and then pulling the best and most popular stuff into core WP.

Release Candidate 1 of WordPress 2.3 was released last night.  It was supposed to go out the night before, but I got caught up with some personal stuff.  We postponed one day and used the extra time to get in a couple more bug fixes.

We have less than a week until the final release of 2.3. Grab RC1 and help us shake out as many bugs as we can.  2.3 is a fairly big release and needs all of the testing it can get.