WordPress Release: 3.4.0

TL;DR

WordPress 3.4 introduces a revolutionary new Theme Customizer that allows users to preview theme changes in real-time before publishing them. This major update also brings improved media handling with flexible header images and background selection from the media library, Twitter embeds, better internationalization support, and numerous performance improvements. The release focuses on enhancing the user experience for theme customization while maintaining backward compatibility.

Highlight of the Release

• Theme Customizer with live preview for making theme changes
• Flexible header images with media library integration
• Twitter content embedding with oEmbed support
• Improved internationalization with better translation loading
• Performance improvements to WP_Query and theme handling

Migration Guide

Theme Developers

If you've created custom themes with header or background customization:

1. Custom Headers: Update your implementation to use the new flexible header system. Review the add_theme_support('custom-header') arguments to take advantage of new features.

2. Custom Backgrounds: If you're using custom backgrounds, ensure your theme properly handles the custom-background class. To allow users to remove default background images, you should structure your CSS like this:

   body {
     background-image: url(...);
   }
   body.custom-background {
     background-image: none;
   }
   

3. Theme Customizer: Consider adding support for the Theme Customizer API to provide live preview options for your theme settings.

4. Internationalization: Add Text Domain and Domain Path headers to your theme's style.css to improve translation handling.

Plugin Developers

1. AJAX Actions: If you're using custom AJAX actions, be aware that WordPress 3.4 changes how action IDs are passed. Review your code if you're hooking into core AJAX actions.

2. Theme Data: If you're using the deprecated get_theme_data() function, note that it now properly supports the 'extra_theme_headers' filter again.

3. SSL Handling: Consider using the new set_url_scheme() function instead of hardcoding HTTP/HTTPS in URLs.

Upgrade Recommendations

Recommended for all users: WordPress 3.4 is a stable release with significant new features and improvements that enhance the user experience without introducing major breaking changes.

Preparation before upgrading:

1. As always, back up your database and files before upgrading
2. Test your themes and plugins in a staging environment if possible
3. Theme developers should review their custom header and background implementations
4. If you're using a highly customized theme, test the Theme Customizer to ensure it works properly with your customizations

After upgrading:

1. Review your theme settings in the new Theme Customizer
2. Check that header and background images display correctly
3. If you use Twitter embeds, test them to ensure proper formatting

This release focuses on enhancing the user experience while maintaining backward compatibility, so most sites should upgrade without issues.

Bug Fixes

Image Caption Handling

• Fixed an issue where image caption labels were incorrectly changed
• Added cache refreshing for Edit Image iframe HTML to ensure proper display
• Fixed closing div position when post doesn't support editor

Theme and UI Fixes

• Fixed path to customizer collapse arrows
• Fixed orphaned arrow on Twenty Eleven's paged post navigation
• Corrected the display of featured images in the showcase template for IE8
• Removed border and padding from images in the image widget in Twenty Eleven
• Added whitespace to paragraphs in the image post format in Twenty Eleven
• Fixed styling for samp and var elements in Twenty Eleven

Admin Interface

• Fixed menu order disambiguation
• Fixed admin menu hover behavior
• Added space between 'Plugins' title and 'Add New' button on plugins.php
• Fixed comment hotkeys for Firefox and IE
• Fixed Quicktags buttons in IE7

Security and Authentication

• Fixed handling of authentication attempts in comments
• Improved handling of SSL for customizer preview
• Fixed cookie handling for domain mapping scenarios

New Features

Theme Customizer

The standout feature of WordPress 3.4 is the new Theme Customizer that allows users to preview theme changes in real-time before publishing them. This powerful tool provides a split-screen interface with controls on the left and a live preview on the right. Users can modify colors, header images, backgrounds, and other theme settings while seeing the changes instantly applied in the preview.

Flexible Header Images

WordPress 3.4 introduces a more flexible header image system that allows themes to define custom image sizes and supports cropping options. Users can now select header images from the media library instead of only being able to upload new ones, making it easier to reuse existing images.

Twitter Content Embedding

Native support for Twitter embeds has been added, allowing users to simply paste a Twitter URL into content to automatically display formatted tweets. This joins the existing oEmbed support for YouTube, Vimeo, and other services.

Media Library Integration for Backgrounds

Similar to header images, background images can now be selected from the media library, providing more flexibility when customizing site appearance.

Improved Theme Experience

The theme browsing and installation experience has been enhanced with better information display and the ability to see translated theme information in the theme browser even for inactive themes.

Security Updates

SSL Improvements

• Added set_url_scheme() function to properly handle HTTP vs HTTPS URLs
• Improved SSL handling for the customizer preview to avoid insecure content warnings
• Updated header and background image sources to respect SSL settings

Authentication Handling

• Improved authentication handling in comment processing to avoid repeated auth attempts
• Enhanced security for AJAX actions by refining how action IDs are passed

Admin Security

• Added protection against unfiltered HTML comments from iframe contexts
• Improved nonce handling for theme switching and network theme enabling

Performance Improvements

Faster WP_Query

WordPress 3.4 includes significant performance improvements to WP_Query, resulting in faster page loads, especially for complex queries.

Theme Handling

The theme system has been optimized to load translations more efficiently, reducing memory usage and improving performance when switching between themes.

Script and Style Compression

Multiple rounds of script and style compression were performed throughout the development cycle, resulting in smaller file sizes and faster loading times.

Customizer Performance

The Theme Customizer was designed with performance in mind, using JavaScript-based previews where possible to avoid full page reloads when making simple changes like color adjustments.

Impact Summary

WordPress 3.4 represents a significant step forward in theme customization capabilities, introducing the Theme Customizer as a cornerstone feature that transforms how users interact with their site's appearance. This release focuses on improving the user experience through real-time previews and enhanced media handling, while also addressing performance and internationalization needs.

The Theme Customizer fundamentally changes the theme customization workflow from a "save and refresh" model to an interactive, real-time preview experience. This not only makes customization more intuitive but also reduces the risk of publishing unwanted changes to live sites.

For developers, the release provides new APIs and functions that improve SSL handling, performance, and internationalization support. Theme developers in particular gain powerful new tools to create more flexible and user-friendly themes.

The addition of Twitter embedding capabilities enhances content creation options, while improvements to media handling make it easier to reuse existing images for headers and backgrounds.

Overall, WordPress 3.4 delivers meaningful improvements to both the user interface and underlying architecture without introducing major breaking changes, making it a recommended upgrade for all WordPress sites.