|Description||Specification of subtitle - its reference name and title - and its content.
The content consists of
a) CDATA text
b) nested subtitles.
Historical: this used to have wintel, unix and images.
The subtitles can nest. The highest-level subtitles are at the 1.1.1 level.
- Wintel/Unix distinction has been eliminated.
- Images are handled in-line now.