This function invokes all functions attached to action hook $tag. It is
possible to create new action hooks by simply calling this function,
specifying the name of the new hook using the $tag parameter.
You can pass extra arguments to the hooks, much like you can with apply_filters().
Example usage:
// The action callback function
function example_callback( $arg1, $arg2 ) {
// (maybe) do something with the args
}
add_action( 'example_action', 'example_callback', 10, 2 );
/*
* Trigger the actions by calling the 'example_callback()' function that's
* hooked onto `example_action` above.
*
* - 'example_action' is the action hook
* - $arg1 and $arg2 are the additional arguments passed to the callback.
$value = do_action( 'example_action', $arg1, $arg2 );