​The `add_custom_background()` function in WordPress allows developers to create custom background displays by calling on specific actions such as `wp_head` or the custom background administration screen

Adds slashes to a string or recursively adds slashes to strings within an array.

Deprecated functionality for activating a network-only plugin.

Handles the display of choosing a user’s primary site.

Attempts activation of plugin in a “sandbox” and redirects on success.

Learn how to convert a mixed data type to a non-negative integer using the 'absint' function in WordPress development

​The `activate_plugins()` function in WordPress is used to activate a single plugin or a list of plugins

​The `clean_attachment_cache()` function in WordPress clears attachments from the cache

Outputs the link to the comments for the current post in an XML safe way.