I could neither find the answers I wanted in the book nor any
explanation about the logic and design of the syntax language.
Retrospectively it appears others added to it.
I recommend the current documentation instead of the 2007 book. There is
a lot of reading, no technical summary of the concept, logic and
structure, but there is a lot in the current documentation that is
missed, in my opinion, from the book.
For the adventurous and wealthy, your best bet is a trip to the USA and
a week long stay with Phil - afterwards you will know an awful lot about
Exim :-)