1. It is possible for "CHAP" frames to describe chapters that overlap or have gaps between them.
  2. It is permitted to include "CHAP" frames that are not referenced by any "CTOC" frames. For example, these might be used to provide images that can be presented in synchronisation with the audio, rather than to support a table of contents.
  3. It is recommended that "CHAP" and "CTOC" frames should include a TIT2 sub-frame to provide a human readable identifier which can be presented to the end-user to aid navigation and selection.