Suggested text to include in Zabbix documentation (largely borrowed from C language standards):

Each of the operators '<' (less than), '>' (greater than), '<=' (less than or equal to), '>=' (greater than or equal to), '=' (equal to), '<>' (not equal to) shall yield 1 if the specified relation is true and 0 if it is false.

The 'and' operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it yields 0.

The 'or' operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it yields 0.

The result of the logical negation operator 'not' is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0.

Knowing exactly how these operators work will allow users to write more complex calculated item and trigger expressions.

//logic_expr ? true_value : false_value
(logic_expr) * (true_value) + (not logic_expr) * (false_value)

//max of two items
(item1 > item2) * item1 + (item1 <= item2) * item2

//number of items over threshold
(item1 > threshold) + (item2 > threshold) + ... + (itemN > threshold)