wp_font_dir()wp-includes/fonts.php | Returns an array containing the current fonts upload directory’s path and URL.
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WP_Block_Bindings_Registry::register()wp-includes/class-wp-block-bindings-registry.php | Registers a new block bindings source.
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WP_REST_Font_Faces_Controller::handle_font_file_upload()wp-includes/rest-api/endpoints/class-wp-rest-font-faces-controller.php | Handles the upload of a font file using wp_handle_upload() .
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_wp_footnotes_kses_init_filters()wp-includes/blocks.php | Adds the filters for footnotes meta field.
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wp_initialize_theme_preview_hooks()wp-includes/theme-previews.php | Add filters and actions to enable Block Theme Previews in the Site Editor.
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_wp_get_iframed_editor_assets()wp-includes/block-editor.php | Collect the block editor assets that need to be loaded into the editor’s iframe.
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WP_REST_Menu_Items_Controller::prepare_item_for_response()wp-includes/rest-api/endpoints/class-wp-rest-menu-items-controller.php | Prepares a single post output for response.
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WP_REST_Global_Styles_Controller::prepare_item_for_response()wp-includes/rest-api/endpoints/class-wp-rest-global-styles-controller.php | Prepare a global styles config output for response.
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_add_default_theme_supports()wp-includes/theme.php | Adds default theme supports for block themes when the ‘after_setup_theme’ action fires.
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wp_enqueue_block_style()wp-includes/script-loader.php | Enqueues a stylesheet for a specific block.
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WP_Widget_Block::__construct()wp-includes/widgets/class-wp-widget-block.php | Sets up a new Block widget instance.
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wp_enqueue_global_styles()wp-includes/script-loader.php | Enqueues the global styles defined via theme.json.
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WP_Sitemaps_Renderer::check_for_simple_xml_availability()wp-includes/sitemaps/class-wp-sitemaps-renderer.php | Checks for the availability of the SimpleXML extension and errors if missing.
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WP_Sitemaps::init()wp-includes/sitemaps/class-wp-sitemaps.php | Initiates all sitemap functionality.
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wp_pre_kses_block_attributes()wp-includes/formatting.php | Removes non-allowable HTML from parsed block attribute values when filtering in the post context.
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enqueue_block_styles_assets()wp-includes/script-loader.php | Function responsible for enqueuing the styles required for block styles functionality on the editor and on the frontend.
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WP_Site_Health::__construct()wp-admin/includes/class-wp-site-health.php | WP_Site_Health constructor.
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wp_init_targeted_link_rel_filters()wp-includes/formatting.php | Adds all filters modifying the rel attribute of targeted links.
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wp_get_active_and_valid_themes()wp-includes/load.php | Retrieves an array of active and valid themes.
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update_sitemeta_cache()wp-includes/ms-site.php | Updates metadata cache for list of site IDs.
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WP_REST_Post_Search_Handler::prepare_item()wp-includes/rest-api/search/class-wp-rest-post-search-handler.php | Prepares the search result for a given post ID.
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do_blocks()wp-includes/blocks.php | Parses dynamic blocks out of post_content and re-renders them.
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_restore_wpautop_hook()wp-includes/blocks.php | If do_blocks() needs to remove wpautop() from the the_content filter, this re-adds it afterwards, for subsequent the_content usage.
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wpdb::placeholder_escape()wp-includes/class-wpdb.php | Generates and returns a placeholder escape string for use in queries returned by ::prepare().
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WP_Widget_Custom_HTML::widget()wp-includes/widgets/class-wp-widget-custom-html.php | Outputs the content for the current Custom HTML widget instance.
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WP_Widget_Media::_register_one()wp-includes/widgets/class-wp-widget-media.php | Add hooks while registering all widget instances of this widget class.
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WP_Widget_Media_Video::render_media()wp-includes/widgets/class-wp-widget-media-video.php | Render the media on the frontend.
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WP_Customize_Manager::save_changeset_post()wp-includes/class-wp-customize-manager.php | Saves the post for the loaded changeset.
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WP_REST_Attachments_Controller::prepare_items_query()wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php | Determines the allowed query_vars for a get_items() response and prepares for WP_Query.
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WP_REST_Posts_Controller::prepare_item_for_response()wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php | Prepares a single post output for response.
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WP_REST_Posts_Controller::get_item_permissions_check()wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php | Checks if a given request has access to read a post.
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WP_REST_Posts_Controller::get_items()wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php | Retrieves a collection of posts.
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WP_REST_Comments_Controller::check_read_post_permission()wp-includes/rest-api/endpoints/class-wp-rest-comments-controller.php | Checks if the post can be read.
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WP_Locale_Switcher::init()wp-includes/class-wp-locale-switcher.php | Initializes the locale switcher.
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WP_Taxonomy::add_hooks()wp-includes/class-wp-taxonomy.php | Registers the ajax callback for the meta box.
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WP_Customize_Nav_Menus::insert_auto_draft_post()wp-includes/class-wp-customize-nav-menus.php | Adds a new auto-draft post.
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WP_Customize_Custom_CSS_Setting::preview()wp-includes/customize/class-wp-customize-custom-css-setting.php | Add filter to preview post value.
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WP_Metadata_Lazyloader::queue_objects()wp-includes/class-wp-metadata-lazyloader.php | Adds objects to the metadata lazy-load queue.
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WP_Customize_Widgets::render_widget_partial()wp-includes/class-wp-customize-widgets.php | Renders a specific widget using the supplied sidebar arguments.
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WP_Customize_Widgets::selective_refresh_init()wp-includes/class-wp-customize-widgets.php | Adds hooks for selective refresh.
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rest_cookie_check_errors()wp-includes/rest-api.php | Checks for errors when using cookie-based authentication.
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rest_api_default_filters()wp-includes/rest-api.php | Registers the default REST API filters.
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wp_handle_comment_submission()wp-includes/comment.php | Handles the submission of a comment, usually posted to wp-comments-post.php via a comment form.
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WP_Screen::render_view_mode()wp-admin/includes/class-wp-screen.php | Renders the list table view mode preferences.
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WP_Customize_Nav_Menu_Setting::update()wp-includes/customize/class-wp-customize-nav-menu-setting.php | Create/update the nav_menu term for this setting.
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WP_Customize_Nav_Menu_Setting::preview()wp-includes/customize/class-wp-customize-nav-menu-setting.php | Handle previewing the setting.
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WP_Customize_Nav_Menu_Item_Setting::update()wp-includes/customize/class-wp-customize-nav-menu-item-setting.php | Creates/updates the nav_menu_item post for this setting.
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WP_Customize_Nav_Menu_Item_Setting::preview()wp-includes/customize/class-wp-customize-nav-menu-item-setting.php | Handle previewing the setting.
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WP_Customize_Nav_Menus_Panel::render_screen_options()wp-includes/customize/class-wp-customize-nav-menus-panel.php | Render screen options for Menus.
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WP_Customize_Nav_Menus::customize_preview_init()wp-includes/class-wp-customize-nav-menus.php | Adds hooks for the Customizer preview.
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WP_Customize_Nav_Menus::customize_register()wp-includes/class-wp-customize-nav-menus.php | Adds the customizer settings and controls.
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WP_Customize_Nav_Menus::__construct()wp-includes/class-wp-customize-nav-menus.php | Constructor.
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WP_Site_Icon::get_post_metadata()wp-admin/includes/class-wp-site-icon.php | Adds custom image sizes when meta data for an image is requested, that happens to be used as Site Icon.
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WP_Site_Icon::__construct()wp-admin/includes/class-wp-site-icon.php | Registers actions and filters.
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wp_ajax_crop_image()wp-admin/includes/ajax-actions.php | Handles cropping an image via AJAX.
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wp_edit_attachments_query_vars()wp-admin/includes/post.php | Returns the query variables for the current attachments request.
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_WP_List_Table_Compat::__construct()wp-admin/includes/class-wp-list-table-compat.php | Constructor.
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login_header()wp-login.php | Outputs the login page header.
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WP_Automatic_Updater::update()wp-admin/includes/class-wp-automatic-updater.php | Updates an item, if appropriate.
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Language_Pack_Upgrader::bulk_upgrade()wp-admin/includes/class-language-pack-upgrader.php | Upgrades several language packs at once.
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Plugin_Upgrader::bulk_upgrade()wp-admin/includes/class-plugin-upgrader.php | Upgrades several plugins at once.
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Theme_Upgrader::check_parent_theme_filter()wp-admin/includes/class-theme-upgrader.php | Checks if a child theme is being installed and its parent also needs to be installed.
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Theme_Upgrader::install()wp-admin/includes/class-theme-upgrader.php | Install a theme package.
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Theme_Upgrader::upgrade()wp-admin/includes/class-theme-upgrader.php | Upgrades a theme.
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Theme_Upgrader::bulk_upgrade()wp-admin/includes/class-theme-upgrader.php | Upgrades several themes at once.
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Plugin_Upgrader::install()wp-admin/includes/class-plugin-upgrader.php | Install a plugin package.
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Plugin_Upgrader::upgrade()wp-admin/includes/class-plugin-upgrader.php | Upgrades a plugin.
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WP_Screen::render_per_page_options()wp-admin/includes/class-wp-screen.php | Renders the items per page option.
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wp_update_core()wp-admin/includes/deprecated.php | This was once used to kick-off the Core Updater.
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wp_update_plugin()wp-admin/includes/deprecated.php | This was once used to kick-off the Plugin Updater.
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wp_update_theme()wp-admin/includes/deprecated.php | This was once used to kick-off the Theme Updater.
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WP_List_Table::__construct()wp-admin/includes/class-wp-list-table.php | Constructor.
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wp_dashboard_setup()wp-admin/includes/dashboard.php | Registers dashboard widgets.
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register_setting()wp-includes/option.php | Registers a setting and its data.
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media_upload_type_form()wp-admin/includes/media.php | Outputs the legacy media upload form for a given media type.
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media_upload_gallery_form()wp-admin/includes/media.php | Adds gallery form to upload iframe.
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media_upload_library_form()wp-admin/includes/media.php | Outputs the legacy media upload form for the media library.
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wp_ajax_query_attachments()wp-admin/includes/ajax-actions.php | Handles querying attachments via AJAX.
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wp_ajax_replyto_comment()wp-admin/includes/ajax-actions.php | Handles replying to a comment via AJAX.
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wp_link_manager_disabled_message()wp-admin/includes/bookmark.php | Outputs the ‘disabled’ message for the WordPress Link Manager.
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WP_Media_List_Table::display_rows()wp-admin/includes/class-wp-media-list-table.php | |
WP_Importer::get_page()wp-admin/includes/class-wp-importer.php | Gets URL.
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WP_Comments_List_Table::__construct()wp-admin/includes/class-wp-comments-list-table.php | Constructor.
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wp_nav_menu_setup()wp-admin/includes/nav-menu.php | Register nav menu meta boxes and advanced menu items.
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wp_list_widget_controls()wp-admin/includes/widgets.php | Show the widgets and their settings for a sidebar.
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WP_Posts_List_Table::display_rows()wp-admin/includes/class-wp-posts-list-table.php | |
do_core_upgrade()wp-admin/update-core.php | Upgrades WordPress core display.
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WP_Customize_Manager::customize_preview_init()wp-includes/class-wp-customize-manager.php | Prints JavaScript settings.
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WP_Customize_Manager::start_previewing_theme()wp-includes/class-wp-customize-manager.php | If the theme to be previewed isn’t the active theme, add filter callbacks to swap it out at runtime.
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WP_Customize_Manager::__construct()wp-includes/class-wp-customize-manager.php | Constructor.
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wp_trim_excerpt()wp-includes/formatting.php | Generates an excerpt from the content, if needed.
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kses_init_filters()wp-includes/kses.php | Adds all KSES input form content filters.
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_default_wp_die_handler()wp-includes/functions.php | Kills WordPress execution and displays HTML page with an error message.
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WP_Widget_Text::widget()wp-includes/widgets/class-wp-widget-text.php | Outputs the content for the current Text widget instance.
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WP_Widget_Text::form()wp-includes/widgets/class-wp-widget-text.php | Outputs the Text widget settings form.
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WP_Embed::__construct()wp-includes/class-wp-embed.php | Constructor
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do_shortcode()wp-includes/shortcodes.php | Searches content for shortcodes and filter shortcodes through their hooks.
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WP_oEmbed::__construct()wp-includes/class-wp-oembed.php | Constructor.
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add_action()wp-includes/plugin.php | Adds a callback function to an action hook.
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WP_Customize_Setting::__construct()wp-includes/class-wp-customize-setting.php | Constructor.
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WP_Customize_Setting::preview()wp-includes/class-wp-customize-setting.php | Add filters to supply the setting’s value when accessed.
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wp_signon()wp-includes/user.php | Authenticates and logs a user in with ‘remember’ capability.
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_set_preview()wp-includes/revision.php | Sets up the post object for preview based on the post autosave.
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_show_post_preview()wp-includes/revision.php | Filters the latest content for preview from the post autosave.
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ms_upload_constants()wp-includes/ms-default-constants.php | Defines Multisite upload constants.
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Walker_Comment::start_el()wp-includes/class-walker-comment.php | Starts the element output.
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WP_Customize_Widgets::start_capturing_option_updates()wp-includes/class-wp-customize-widgets.php | Begins keeping track of changes to widget options, caching new values.
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WP_Customize_Widgets::capture_filter_pre_update_option()wp-includes/class-wp-customize-widgets.php | Pre-filters captured option values before updating.
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WP_Customize_Widgets::__construct()wp-includes/class-wp-customize-widgets.php | Initial loader.
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WP_Customize_Widgets::override_sidebars_widgets_for_theme_switch()wp-includes/class-wp-customize-widgets.php | Override sidebars_widgets for theme switch.
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WP_Customize_Widgets::customize_register()wp-includes/class-wp-customize-widgets.php | Registers Customizer settings and controls for all sidebars and widgets.
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wp_update_comment()wp-includes/comment.php | Updates an existing comment in the database.
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check_comment_flood_db()wp-includes/comment.php | Hooks WP’s native database-based comment-flood check.
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register_meta()wp-includes/meta.php | Registers a meta key.
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_WP_Editors::editor()wp-includes/class-wp-editor.php | Outputs the HTML for a single instance of the editor.
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Example: Let’s add extra sections to TwentySeventeen Front page.
By default, TwentySeventeen theme has 4 sections for the front page. This example will make them 6
To pass a variable to the called function of the filter, you can use closures (since PHP 5.3+) when the argument is not available in the original coded apply_filters. For example:
Example: Let display custom length of post excerpt.
By default, WordPress display 57 character. you can set custom length using above code. this time except length will be 40. it is a nice and easiest use of add_filter.
Example: If you want to inject a CLASS/ID CSS in content. Let’s add extra CLASS/ID to post content.
In the special case you have to add a filter before WordPress starts, you can create and pre-populate the global
$wp_filter
array instead of using the not-yet availableadd_filter
(oradd_action
) function:WP_Hook::build_preinitialized_hooks
will automatically take care of the rest.Though to remove your filter, you can only use the remove_all_filters() function.
The Callback
$function_to_add
need not be defined until the Filter hook fires. This means that:add_filter
function does not check that$function_to_add
existsfunction
statement for$function_to_add
can be defined after theadd_filter
statement, even in a conditional (e.g. –if
block) where the$function_to_add
function does not actually exist until after theadd_filter
function executesPoint 3 needs to be considered during Testing or Quality Control
An undefined $function_to_add function detected when a Filter hook fires is reported as a Warning error:
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'reg_public1' not found or invalid function name in /var/www/example.com/public_html/wp-includes/class-wp-hook.php on line 288
Example
The filter
img_caption_shortcode
is applied inmedia.php
using the following call:The target filter function will be called with three arguments:
” <= This is normally the value the filter will be modifying
$attr
$content
In order for the filter function to actually receive the full argument list, the call to
add_filter()
must be modified to specify there are 3 arguments on the parameter list.