Web Design Leaves

<footer>
  <!-- my_footer_action_hook と言う名前のアクションフックを設置 -->
  <?php do_action( 'my_footer_action_hook' ); ?>
</footer>

//functions.php
//アクションの登録
add_action( 'my_footer_action_hook', 'my_footer_echo' );
//実行するアクションの定義
function my_footer_echo(){
  echo 'This is my action hook!';
}

add_action( 'my_footer_action_hook', function(){
    echo 'This is my action hook!';
});

add_action( 'my_footer_action_hook', 'my_footer_echo' );
function my_footer_echo(){
    echo 'This is my action hook!';
}

add_action( 'my_footer_action_hook', 'my_footer_echo2' );
function my_footer_echo2(){
    echo 'This is my action hook #2!';
}

function my_footer_echo(){
  do_action( 'my_footer_echo' );
}

//アクション関数をフック my_footer_echo に登録
add_action( 'my_footer_echo', 'my_footer_link_top' );
function my_footer_link_top(){ //実行するアクションの定義
  echo '<a href="#">Top</a><br>';
}

//アクション関数をフック my_footer_echo に登録
add_action( 'my_footer_echo', 'my_footer_link_cat' );
function my_footer_link_cat(){ //実行するアクションの定義
  echo '<a href="cat.php">Cat</a><br>';
}

<p><?php my_footer_echo(); ?></p>

<!-- 以下が出力されます。-->
<a href="#">Top</a><br>
<a href="cat.php">Cat</a><br>

/**
 * Fire the wp_head action. （wp_head アクションを発火させる）
 *
 * See {@see 'wp_head'}.
 *
 * @since 1.2.0
 */
function wp_head() {
  /**
   * Prints scripts or data in the head tag on the front end.
   *
   * @since 1.5.0
   */
  do_action( 'wp_head' );
}

// Actions
add_action( 'wp_head', '_wp_render_title_tag',            1     );
add_action( 'wp_head', 'wp_enqueue_scripts',              1     );
add_action( 'wp_head', 'wp_resource_hints',               2     );
add_action( 'wp_head', 'feed_links',                      2     );
add_action( 'wp_head', 'feed_links_extra',                3     );
add_action( 'wp_head', 'rsd_link'                               );
add_action( 'wp_head', 'wlwmanifest_link'                       );
add_action( 'wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0 );
add_action( 'wp_head', 'locale_stylesheet'                      );
・・・省略・・・

//wp-settings.php に記述されている do_action() の抜粋
/* Fires once all must-use and network-activated plugins have loaded. */
do_action( 'muplugins_loaded' );
・・・
/* Fires once activated plugins have loaded. */
do_action( 'plugins_loaded' );
・・・
/* Fires before the theme is loaded. */
do_action( 'setup_theme' );
・・・
//Load the functions for the active theme（functions.php の読み込み）
if ( ! wp_installing() || 'wp-activate.php' === $pagenow ) {
  if ( TEMPLATEPATH !== STYLESHEETPATH && file_exists( STYLESHEETPATH . '/functions.php' ) )
    include( STYLESHEETPATH . '/functions.php' );
  if ( file_exists( TEMPLATEPATH . '/functions.php' ) )
    include( TEMPLATEPATH . '/functions.php' );
}
 
/* Fires after the theme is loaded */
do_action( 'after_setup_theme' );
・・・
/*
Fires after WordPress has finished loading but before any headers are sent.
Most of WP is loaded at this stage, and the user is authenticated. 
WP continues to load on the {@see 'init'} hook that follows (e.g. widgets), and many plugins instantiate themselves on it for all sorts of reasons (e.g. they need a user, a taxonomy, etc.).
If you wish to plug an action once WP is loaded, use the {@see 'wp_loaded'} hook below.
 */
do_action( 'init' );
・・・
/*  This hook is fired once WP, all plugins, and the theme are fully loaded and instantiated. */
do_action( 'wp_loaded' );

//default-filters.php 一部抜粋
// Theme
add_action( 'wp_loaded', '_custom_header_background_just_in_time' );
add_action( 'wp_head', '_custom_logo_header_styles' );
add_action( 'plugins_loaded', '_wp_customize_include' );
add_action( 'transition_post_status', '_wp_customize_publish_changeset', 10, 3 );
add_action( 'admin_enqueue_scripts', '_wp_customize_loader_settings' );
add_action( 'delete_attachment', '_delete_attachment_theme_mod' );
add_action( 'transition_post_status', '_wp_keep_alive_customize_changeset_dependent_auto_drafts', 20, 3 );

// Calendar widget cache
add_action( 'save_post', 'delete_get_calendar_cache' );
add_action( 'delete_post', 'delete_get_calendar_cache' );
add_action( 'update_option_start_of_week', 'delete_get_calendar_cache' );
add_action( 'update_option_gmt_offset', 'delete_get_calendar_cache' );

// Author
add_action( 'transition_post_status', '__clear_multi_author_cache' );

// Post
add_action( 'init', 'create_initial_post_types', 0 ); // highest priority
add_action( 'admin_menu', '_add_post_type_submenus' );
add_action( 'before_delete_post', '_reset_front_page_settings_for_post' );
add_action( 'wp_trash_post',      '_reset_front_page_settings_for_post' );
add_action( 'change_locale', 'create_initial_post_types' );

// Post Formats
add_filter( 'request', '_post_format_request' );
add_filter( 'term_link', '_post_format_link', 10, 3 );
add_filter( 'get_post_format', '_post_format_get_term' );
add_filter( 'get_terms', '_post_format_get_terms', 10, 3 );
add_filter( 'wp_get_object_terms', '_post_format_wp_get_object_terms' );

// KSES
add_action( 'init', 'kses_init' );
add_action( 'set_current_user', 'kses_init' );

// Script Loader
add_action( 'wp_default_scripts', 'wp_default_scripts' );
add_action( 'wp_enqueue_scripts', 'wp_localize_jquery_ui_datepicker', 1000 );
add_action( 'admin_enqueue_scripts', 'wp_localize_jquery_ui_datepicker', 1000 );
add_action( 'admin_print_scripts-index.php', 'wp_localize_community_events' );
add_filter( 'wp_print_scripts', 'wp_just_in_time_script_localization' );
add_filter( 'print_scripts_array', 'wp_prototype_before_jquery' );
add_filter( 'customize_controls_print_styles', 'wp_resource_hints', 1 );

add_action( 'wp_default_styles', 'wp_default_styles' );
add_filter( 'style_loader_src', 'wp_style_loader_src', 10, 2 );

// Taxonomy
add_action( 'init', 'create_initial_taxonomies', 0 ); // highest priority
add_action( 'change_locale', 'create_initial_taxonomies' );

// Canonical
add_action( 'template_redirect', 'redirect_canonical' );
add_action( 'template_redirect', 'wp_redirect_admin_locations', 1000 );

// Shortcodes
add_filter( 'the_content', 'do_shortcode', 11 ); 

function my_template_tag($text) {
  $text = "My text: " . $text;
  return apply_filters( 'my_filter_hook', $text );
}

<p><?php echo my_template_tag("test"); ?></p>
<!--　My text: test と出力される　-->

function my_filter_callback($text) {
  return "Hello ! ". strtoupper($text);
}
add_filter('my_filter_hook', 'my_filter_callback');

<p><?php echo my_template_tag("test"); ?></p>
<!--　Hello ! MY TEXT: TEST と出力される　-->