WordPress classes explained

Question

Are there any books, websites or lectures that explain the built-in WordPress classes? I would really like to learn how WordPress works internally.

I've dug up the core files on trac and even went through the class reference on codex but yet I find it difficult to learn this way.

I know this is not a place to be asking for resources but everywhere I search the results are theme/plugin tutorials. I really want to understand the internal working of WordPress, can anyone give me pointers to go ahead with this? My PHP skills are just above intermediate

Answer 1

https://developer.wordpress.org/reference/ is sometimes more useful or other links on that page like Getting Started with WordPress. But you're better off with running Query Monitor to see what is happening on each page then looking up the concepts individually. I don't think anyone learns WP in a day. I think they typically focus on a single topic at a time after referencing existing themes and plugins. GenerateWP can jumpstart you in a better direction as well by creating well-form code.

Part of the journey to learn is being able to see what is happening when you test new ideas. I highly recommend the tools below.

• Query Monitor - Visualize Hooks/Queries/and more
• Debug Bar
• Debug Bar Console - ASYNC PHP console
• Kint Debugger - Visualize Debug Data
• Debug Meta Data - Visualize Post Meta Data
• Monkeyman Rewrite Analyzer - Visualize URL Rewrite Rules
• WordPress Admin Styles - Shows the WordPress admin styles
• WordPress Media Javascript Guide - Interactive documentation for the Javascript powering WP Media
• WP REST API - Access your WordPress site's data through an easy-to-use HTTP REST API
• WP-CLI - Interact with WordPress through the command line
• WordPress Core Code - WordPress on GitHub -- faster to browse than Trac
• WordPress Slack Channels - Chat about WP Core or just observe the conversations
• WordPress Support - Forum for support
• PHP CodeSniffer + WordPress Rules - Find errors in your code
• APIGen - Auto Generate Documentation from your code
• Basic WordPress Vagrant - Simple boxes to test simple sites with

Good Stack Exchange Answers;

• When should you use WP_Query vs query_posts() vs get_posts()?
• Between functions.php, widgets and plugins, which is loaded first?
• Is there a flowchart for WordPress loading sequence?
• Where is the right place to register/enqueue scripts & styles
• What are PHP extensions and libraries WP needs and/or uses?
• Menu items description? Custom Walker for wp_nav_menu()
• Need a simple but complete example of adding metabox to taxonomy
• Adding Custom Text Patterns in the WP 4.5 Visual Editor
• Correct regex for wp_embed_register_handler
• Using rewrite rule to access a view of a plugin from home page
• Can I programmatically login a user without a password?
• How to remove a filter that is an anonymous object?
• How to mix partial and full page refresh in the same section of the customizer?
• https://codex.wordpress.org/Plugin_API/Action_Reference
• https://10up.github.io/Engineering-Best-Practices/php/#performance

Interactive diagram for the template hierachy

Answer 2

I suggest you the following approach. You download WordPress. Use the Text editor with the search feature, like Atom-editor, or Sublime and read the comments. You may get the idea about what classes exists, and how they came in to WordPress.

/**
 * Requests for PHP
 *
 * Inspired by Requests for Python.
 *
 * Based on concepts from SimplePie_File, RequestCore and WP_Http.
 *
 * @package Requests
 */
class Requests {

This one came into WordPress from the author that also works on SimplePie project and works on REST API.

Find the author, watch the videos, and you will soon know more than you can imagine.