'Similar to' doesn't provide anything concrete to the reader. There was a thread on [Hackers] back in 2015 proposing some docs to clearly explain that ordering is preserved and I am keen to write the documentation if it's agreed to be worth doing.
Haven't reviewed the discussions recently but my understanding is that the lack of guarantee is correct and intentional. There is none. Though we are allergic to writing that out explicitly. Observations that aren't documented are not guaranteed.