The files of WordPress characterize many helpful PHP functions. A portion of the functions, known as Template Tags, are characterized particularly for use in WordPress Themes. There are likewise a few functions identified with actions and filters (the Plugin API), which are in this way utilized principally for creating Plugins. The rest are utilized to make the core WordPress functionality. Huge numbers of the core WordPress functions are helpful to Plugin and Theme developers.
Function : Deprecated functionality for activating a network-only plugin.
Function : Add a user to a blog based on details from maybe_add_existing_user_to_blog().