I understand how to use individual tests and multiples that all return the same state (just use AND or OR in subsequent tests, but I am not clear about more complex variations on this. I want to construct something like this:-

if
a is true
and b is true
or c is true
then…

In order to get this working correctly, it is necessary to know the order of priority for the AND and the OR parts. Do ANDs have priority and then the OR is tested, or the other way around? Or indeed are they taken in strict order of the declaration?

Correct there is no 'look ahead'. Every statement proceeds to the next. The fact that it may modify the test state is not an exception.

The most common errors are: Starting a test sequence with an AND or OR; and inserting a Set where they should be using an AND or OR.

Some statements are smart enough to skip the testing entirely when using AND or OR but that is what you'd expect.

If you have anything complicated enough that you need out of order precedence, the test state can be copied to a variable and used in a subsequent test.