I did look at the code :-)

The enter() method just calls enterabs() with an absolute time calculated from the current time (using the timefunc for the scheduler) and the passed relative time.  Two calls of enter() with the same relative time will therefore use different absolute times unless you're using custom time function with a lower resolution. 

Prorities are only used when who events are scheduled for the same absolute time, which is easy to arrange for using enterabs() but less so using enter() but still can happen when using calculated timeout values.

I don't agree about the example in the documentation, it is a clear demonstration about how to use the API in general and AFAIK is not intended to show how priorities work.