I cant find the tag

Hello and thank you very much for reading this.

I am trying to modify a site and plugins I didn’t created. The plugin receives events from a paying system and basically I want to change the payment status on my site.

My problem, I think, is that I can’t find the functions called below..
The functions that I can’t find anywhere on the site for example are:

should_update_payment_status Called through apply_filters

and most important

before_payment_status_change called with do_action

Here is the code:

function update_payment_status( $payment_id, $new_status = 'publish' ) {
	if ( $new_status == 'completed' || $new_status == 'complete' ) {
		$new_status = 'publish';
	}

	$payment = get_post( $payment_id );

	if ( is_wp_error( $payment ) || !is_object( $payment ) )
		return;

	$old_status = $payment->post_status;

	if ( $old_status === $new_status )
		return; // Don't permit status changes that aren't changes

	$do_change = apply_filters( 'should_update_payment_status', true, $payment_id, $new_status, $old_status );

	if( $do_change ) {

		do_action( 'before_payment_status_change', $payment_id, $new_status, $old_status );

		$update_fields = array( 'ID' => $payment_id, 'post_status' => $new_status, 'edit_date' => current_time( 'mysql' ) );

		wp_update_post( apply_filters( 'update_payment_status_fields', $update_fields ) );

		do_action( 'update_payment_status', $payment_id, $new_status, $old_status );

	}
}

Thank you again. If I am not clear at something please let me know.