They're restricted to only escaping currently active stack frames, not jumping anywhere like full continuations. They're basically equivalent to having a default cascade of

    if (ret == -1) return -1;

after every function invocation, which is why I was calling that aspect a syntactic feature.

It's this implicit return after every function that trips people up (when prematurely exiting from stateful computation). So what I was saying that making the call of an exception-throwing function (slightly) more verbose would alleviate that and pay for the complexity where it was used.