Version 6.3 seems to be event-driven:
////////////////////////////////////////////////// ////////////////////////////////////////////////////////////////////////////
//
// Function: OnFirstUIBefore
//
// Event: FirstUIBefore event is sent when installation is run for the first
// time on given machine. In the handler installation usually displays
// UI allowing end user to specify installation parameters. After this
// function returns, ComponentTransferData is called to perform file
// transfer.
//
////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////////////
OnFirstUIBefore() is executed when the installation is first run on a computer.
////////////////////////////////////////////////// ////////////////////////////////////////////////////////////////////////////
//
// Function: OnFirstUIAfter
//
// Event: FirstUIAfter event is sent after file transfer, when installation
// is run for the first time on given machine. In this event handler
// installation usually displays UI that will inform end user that
// installation has been completed successfully.
//
////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////////////
OnFirstUIAfter() runs after file copying is finished.