2.10. PGC in titles
Following are excerpts from the Unofficial DVD specifications Guide 2.2 ebook.

...A video title often is a unique sequence of video and audio contents. A typical DVD disc contains one or more titles. The longest title often is the main movie on a commercial DVD. A title may have more than one PGCs. PGCs that belong to the same title has the same title number in their header. This document uses the convention and graphical symbol to display a title as shown in the following illustration, representing its data structure as defined by the DVD specifications. From a hierarchy perspective, a title is a level higher than the PGCs...

...In the following project, there are requirements to show the audience three choices of viewing different versions of a documentary video. The documentary video has five different topics. Each topic is organized as a cell. Each cell which represents the video and audio clip of the corresponding topic is uniquely identified by its VOB Id (a number from 1 to 65535). In the following illustration, the cells are labeled from vob.id1 to vob.id5...

...A title containing three PGCs can be designed to allow three different choices of viewing. The first PGC (labeled PGC 1) presents the first choice of viewing. If this is the default choice, when the title is selected, PGC 1 will play back the cells labeled vob.id1, vob.id2, vob.id3, and vob.id4, in that order. PGC 1 is marked as the entry-PGC in the title so when the title is selected, the DVD player knows which PGC to select to begin playback. A title can have as many PGCs as needed, but there can be only one entry-PGC per each title...

Explanations of usage of a group of PGCs in titles are illustrated in the Unofficial DVD specifications Guide 2.2 ...