- a non-nul integer (e.g. '1'), always returns "true".
- a predicate optionally followed by argument(s) in parenthesis.
- a condition placed between a pair of parenthesis '(' and ')'
- - a question mark ('!') preceding any of the non-empty elements above, and
- which will negate its status.
+ - an exclamation mark ('!') preceding any of the non-empty elements above,
+ and which will negate its status.
- expressions combined with a logical AND ('&&'), which will be evaluated
from left to right until one returns false
- expressions combined with a logical OR ('||'), which will be evaluated