Debugging WordPress Core: Actions and Filters

Most WordPress developers are familiar with the concept of actions and filters. At the very heart of WordPress, these hooks allow developers to extend the functionality of WordPress in numerous ways. Whether you want to run a process when a post is saved, add a new section to the Edit User page, or modify the SQL used when querying the database, WordPress has hooks for (almost) everything. One thing I’ve noticed a lot, as a frequent user of the WordPress StackExchange, is that many developers don’t know where to start when trying to figure out which actions or hooks might be available to them. In this blog post, I want to help walk through the process of tracking down various hooks with examples of when you might want to use them and how to implement them.
Actions and Filters: What’s the Difference?
This is a very basic mistake I see often when helping people figure out their WordPress issues. They want to modify the Query with the pre_get_posts filter, but they can’t figure out why their code isn’t modifying anything. Well, let’s take a look at a basic example that sets the post_type parameter to “page”:
add_action( ‘pre_get_posts’, function(
Source: https://managewp.org/articles/18320/debugging-wordpress-core-actions-and-filters

source https://williechiu40.wordpress.com/2019/01/22/debugging-wordpress-core-actions-and-filters/