Apple DVD Studio Pro 4 - Manual (Page 479)

For example, when you assign a connection to a menu, you can choose to jump to a
specific button or to the menu root with no button specified (using the [Menu] selection).
A pre-script assigned to a menu only runs if the element that jumped to it had [Menu]
selected. If the jump selected a specific button on the menu, the pre-script is skipped.
Similarly, a pre-script on a track or story does not run if you jump directly to a marker.
With slideshows, the pre-script does not run if you jump directly to a slide.
In all cases, if you want the pre-script to run, you must jump to the root of the element,
indicated by the square brackets.
If an element is also configured with a display condition, the pre-script runs first, and then
the display condition.
Note: Unlike pre-scripts, display conditions run when any part of an element is connected
to.
Scripting Overview
Scripts you add to your project contain commands that allow you to access the
functionality available in all DVD players. Each script can contain up to 124 commands.
Every DVD player contains a micro-controller that can execute a set of commands defined
by the DVD-Video specification.
The commands defined in the DVD-Video specification are at the level of microprocessor
machine code, with very simple commands used to initiate desired functions. You may
find that some of the concepts and terms are a challenge. Therefore, when learning
scripting, proceed with initial deliberateness and caution—it is very easy to author titles
with scripts that just don’t work. You should also use the Simulator and test builds of
your project using the Apple DVD Player to verify that your title plays back exactly as
intended.
About DVD Player Registers
Each DVD player has two types of memory registers: General Purpose Register Memories
(GPRMs, also known as variables) and System Parameter Register Memories (SPRMs).
Scripts interact with these registers to determine DVD player settings (such as language
and parental control) and to control various aspects of disc playback.
479 Chapter 20 Creating Scripts