I am trying to understand what a plugin does and i see this action
`add_action( 'woocommerce_view_order', __CLASS__ . ':: ' );`
I want to know what it means.
For example i know that the code below means that on action "woocommerce_email_before_order_table" you have to execute the function "show_tracking_number_on_order_completed_email()" in this self class. and I can find the function show_tracking_number_on_order_completed_email() in the class. But in the first instruction there is no function.
add_action( 'woocommerce_email_before_order_table', __CLASS__ . '::show_tracking_number_on_order_completed_email' );