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I am a beginner with WordPress. Studying hook, add_action() and add_filer() and see in the documentation that

add_action( string $tag, callable $function_to_add, int $priority = 10, int $accepted_args = 1 )

But I dont know how to get $tag and where to get it to fill into add_action() or add_filter() function? Thank you.

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  • $tag is just a variable, nothing more. You can also think of it as "first argument passed to add_action()". So when the text references $tag, it means the first argument .. It often helps (me) to see the code examples where this is used, like add_action('init', 'wpse_my_init_function');, etc. Anyway, this is probably too broad/off topic for this plattform
    – kero
    Sep 16, 2017 at 11:29
  • Thank you. And in your example, it is 'init'. But how can I get 'init' value? I mean I can find it it which file? or it is a function in somewhere? Sep 16, 2017 at 11:33
  • You just set it, there are many standard hooks/filters and good plugins include them as well. I really recommend you read more up on WP (either in the doc or using a tutorial online)
    – kero
    Sep 16, 2017 at 11:34

2 Answers 2

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These 2 function add_action() and add_filter() are magics of WP and do not directly affect your code. In WordPress, they use hooks for mocking into existing functions, methods without changing it's code.

The $tag you are referring is the name of the hook that you want to use. List of core hooks can be found here https://codex.wordpress.org/Plugin_API/Hooks. However you can easily create for own hooks. E.g.:

  • When you create a theme, and you want to allow others to add some additional HTML after your header, you may create this snippet:

in functions.php (or in you lib)

function get_custom_header($tag){
    get_header($tag);
    do_action('after_template_header', $tag); // Add $tag as param, this $tag is not
}

in index.php (in theme) or in any theme file

<?php get_custom_header(); // instead of get_header(); ?>

For hooking, others need to add this: ($tag you are asking is 'after_template_header' for this case)

add_action('after_template_header', 'hook_to_header', 10, 1); // 4th param tell WP to use 1 arguments, if you put it 0, you will not need to pass $tag to function
function hook_to_header($tag) {
    echo "After header with tag '$tag' text here";
}

Hope this can help you learning WP well my fellow. Good understand on hooks will help you to do advanced development on WP.

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You are asking how to replace your $tag in add_action function.

Actually the $tag can replace with Hooks ( terminology used by WordPress ) and in function add_action() they write general syntax and use tag instead of Hook. These hooks have Names which are String type and can be replaced according to your need.

Here is a Hook after_header_theme which can be used as a tag in add_action() as

add_action('after_setup_theme','title_helper');
  • after_setup_theme is a Hook provided by WordPress ( $tag according to function syntax )
  • title_helper is custom function

Means upon setting up the theme title_helper function will call and you can fill title_helper function according to your need.

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