An introduction to one of the greatest features of WordPress: Extensibility. Developers area able to use plugins and themes to extend the power of WordPress through a flexible set of APIs. These APIs include pluggable functions, action and filter hooks, and metadata.

1. CSI:
Getting Into the Guts
WordCamp Birmingham, January 14, 2012

2. CSI:
Getting Into the Guts
WordCamp Birmingham, January 14, 2012

3. Version 0.5
Please note that due to unforeseen events, I did not
complete this slide deck to my satisfaction before
presenting it at WordCamp Birmingham.
I will be doing this presentation again at WordCamp
Atlanta, with an improved version of these slides. At that
time, I will replace this presentation with the new,
improved version which will contain more concrete
developer information, code samples, and more
comprehensive pointers to resources.
Thank you for your understanding.
-- Dougal

4. WordPress
Rocks!

5. WordPress
Rocks!
Why?

6. Extensibility
WordPress can do just about any
freaking thing you can think of

7. Extensibility

8. Extensibility
✤ Rich developer APIs

9. Extensibility
✤ Rich developer APIs
✤ Themes

10. Extensibility
✤ Rich developer APIs
✤ Themes
✤ Plugins

11. API

12. API
✤ Application Programming
Interface

13. API
✤ Application Programming
Interface
✤ “...a source code based
specification intended to be
used as an interface by
software components to
communicate with each
other.” – Wikipedia

14. What kind of APIs?
✤ Pluggable functions
✤ Hooks
✤ Actions and Filters
✤ Metadata
✤ Post meta, User meta, Comment meta, Site Options
✤ Custom Javascript and CSS

15. Pluggable
Functions
Login/Cookie/User info
Email notifications, wp_mail()
Security: nonces, password salts &
hashes
Avatars
Display of revision diffs

16. Themes
✤ Sidebars and Widgets
✤ Custom Headers and
Backgrounds
✤ Custom Post Types and
Taxonomies

17. Plugins

18. Plugins
✤ Plugins can do... practically anything:

19. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages

20. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages
✤ Integrate 3rd party data (Twitter, Facebook, etc.)

21. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages
✤ Integrate 3rd party data (Twitter, Facebook, etc.)
✤ Extend user info

22. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages
✤ Integrate 3rd party data (Twitter, Facebook, etc.)
✤ Extend user info
✤ Use Roles & Capabilities to control access to features

23. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages
✤ Integrate 3rd party data (Twitter, Facebook, etc.)
✤ Extend user info
✤ Use Roles & Capabilities to control access to features
✤ Create workflows (e.g., EditFlow plugin)

24. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages
✤ Integrate 3rd party data (Twitter, Facebook, etc.)
✤ Extend user info
✤ Use Roles & Capabilities to control access to features
✤ Create workflows (e.g., EditFlow plugin)
✤ Alternative login systems (LDAP, SSO)

25. Plugins
✤ Plugins can do... practically anything:
✤ Modify posts/pages
✤ Integrate 3rd party data (Twitter, Facebook, etc.)
✤ Extend user info
✤ Use Roles & Capabilities to control access to features
✤ Create workflows (e.g., EditFlow plugin)
✤ Alternative login systems (LDAP, SSO)
✤ The sky’s the limit!

26. Actions
Actions are events
Use them to DO something, rather
than to CHANGE something

27. Actions
plugins_loaded()
setup_theme()
wp_init()
template_redirect()
wp_head()
wp_footer()
http://andy.wordpress.com/2008/10/30/wordpress-include-stack/

28. Filters
Modify existing content
<?php
add_filter( ‘the_content’, ‘lolify’ );
function lolify( $text_in ) {
$text out = do_cool_stuff( $text_in );
return $text_out;
}
?>

29. Metadata
Lets you add additional details beyond
what WordPress provides out-of-the-
box.

30. Metadata
✤ “Data about Data”
Lets you provide additional
details that may or may not be
visible on the site.

31. Putting it
together
✤ codex.wordpress.org
✤ make.wordpress.org
✤ wpdevel.wordpress.com

32. Who are you?
Dougal Campbell
@dougal
dougal.us /
dougal.gunters.org
dougal.campbell@gmail.com