WP extension (enhancement) (tag)

add_theme_support()

Registers support for new theme features in WordPress (support for thumbnails, post formats, etc.).

register_post_meta()

Registers a meta key for posts (post custom field).

register_post_status()

Function for creating a new or editing an old post status, based on the provided parameters.

register_post_type()

Creates a new post type or changes an existing one.

register_taxonomy()

Creates a new custom WordPress taxonomy. Allows you to change an existing taxonomy.

register_term_meta()

Registers a meta-field for the specified taxonomy.

wp_install_defaults()

Creates default content for a newly installed site: basic categories, posts, pages, etc.