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Plugins are tools to extend the functionality of WordPress. The core of WordPress is designed to be lean, to maximize flexibility and minimize code bloat. Plugins offer custom functions and features so that each user can tailor their site to their specific needs.
This article is a comprehensive list of resources related to plugins and plugin development.
General Plugin References
Plugin Development Basics
Plugin Development - Reference
- PHPXref for WordPress - Cross reference of WordPress files, functions, and variables, which seems to point to the latest released version. This redalt.com PHPXref site has the bleeding-edge Trunk version, as well as 1.5 and 2.0, but the Trunk version may not be updating any more. So, there is now a new Trunk Xref site on ftwr.co.uk available.
- Skippy's list of actions and filters
- WordPress Hooks Database, a database of all WordPress' hooks, showing which version they come from, and linking to the source code spots that use them
- Angsuman's list, a comprehensive listing of WordPress action hooks with documentation and source code location information. It contains all documented and undocumented action hooks in WordPress 2.0.
- dd32's wordpress.org/extend Plugin API information
- PHP Cross Reference of the WordPress and BBPress source, using PHPXref by Joost de Valk - also includes tutorial
- WordPress Plugin Development - Beginner's guide
Plugin Development - Special Topics
- Creating Admin Themes - How to create a Plugin that changes the look of the Admin section
- Creating Tables with Plugins - How to store your plugin's data in a new table in the WordPress database
- Custom Queries - How to implement custom queries that let a plugin control which posts are displayed and in what order
- AJAX in Plugins - How to add AJAX functionality to your plugin, in the administration screens or viewer-facing pages
- Creating Options Pages - How to easily create custom options pages and have WordPress do all the hard work for you!
- Modifying Options Pages - How to modify already existing options pages by adding options for your use on them
- Using the add_meta_box() Function - How to add a custom section to the post editing screen, and save the data the user enters
- TinyMCE Custom Buttons - How to add functionality to the TinyMCE Visual/HTML editor for post/page content
- Geodata - Interoperability conventions for plugins that use or manipulate location or geographic data