Following are excerpts from the Unofficial DVD specifications Guide 2.2 ebook.

...Most DVD players can locate a title, and individual chapters or programs in the title. Many remote control units have the GoTo key to support the selection of available titles on the video disc. For instance, pressing GoTo and the number 1 on the keypad selects title 1. Most remote control unit has the Repeat key to repeat the playback of a title, a chapter, or a program...

In summary, chapters in a title are located by two unique items: the PGC in the title and the program in the specified PGC. Chapters are not restricted to be a part of one PGC...Why a chapter is commonly called a Part-Of_Title (PTT) is explained in the Unofficial DVD specifications Guide 2.2 ...

2.11. Graphical display of titles and PGCs

...The above illustration displays two yellow icons representing the titles labeled "Title 1" and "Title 2". Theoretically, a title can have up to 64k PGCs, but the DVD specifications limit a title to a maximum of 999 PGCs. For most practical purposes, there are very few commercial movie DVDs having more than 250 PGCs per title. PGCs are numbered from 1 within each title. Each title must have at least one PGC and can have only one entry-PGC...

...There are virtual commands designed to operate on titles so any title can be located and branched to quickly. The DVD specifications permit up to 99 titles per disc. More details are explained in the Unofficial DVD specifications Guide 2.2 ...