3.2. First-Play Domain
Following are excerpts from the Unofficial DVD specifications Guide 2.2 ebook.

...The first-play domain usually consists of a single PGC called the first-play PGC. When a disc is inserted into the DVD player, all contents of the general parameter registers (GPRM) are set to 0 and the system parameter registers (SPRM) are reset to their default values, then the pre-commands of the first-play PGC are executed. If the post-commands are present in the first-play PGC, they are executed after the pre-commands. Most commercial DVDs use the first-play command to do some setup initializations, checking for regions, display warning screens or other short introduction video contained in PGCs in the VMG domain, and then transfer the playback to a title in a VTS domain or a menu in a VTSM domain...

3.3. Graphical display of First-Play domain

...The above illustration visualizes the First-Play domain with the picture of a generic user remote control unit. When power is pressed to turn on the DVD player, if there is a DVD video disc, its first-play PGC is played back. The first-play PGC of most commercial DVD titles has a precommand section which contains one of the following types of virtual commands...

The above illustration is explained in the Unofficial DVD specifications Guide 2.2 ...

3.4. Virtual commands in First-Play domain
The following virtual commands are available in the first-play domain:

VM Command	Description
1. Nop	No Operation.
2. GoTo	Go to a specified command line.
3. Break	Exit the current command section.
4. Exit	Terminate the playback of a video DVD.
5. JumpTT	Jump to a video title.
6. JumpSS	Jump to a PGC in System Space.
7. SetGPRM	Define contents of a GPRM register.
8. SetGPRMMD	Set GPRM register/counter mode.
9. SetHL_BTN	Set Highlight Menu Button.
10. SetAMXMD	Set Audio Mixing Mode for Karaoke.