Definition/Documentation of "|" in mini notation

Hi. In some performance I've seen "[a|b|c]" apparently for making a (pseudo) random choice. It's currently not in https://tidalcycles.org/Mini_notation_syntax .

I see the implementation (https://github.com/tidalcycles/Tidal/blob/main/src/Sound/Tidal/ParseBP.hs#L409) but it's hard to deduce the intention, in particular, the interaction with other features of the notation, as in

*** Exception: Syntax error in sequence:
  "[0|1|2,3|4|5]"
         ^  
unexpected ","

I am not seeing any test cases (I looked in ParseTest.hs). If you could post some (here), I can collect them into a PR for the repo.

It is a semantical function? The implementation
(https://github.com/tidalcycles/Tidal/blob/main/src/Sound/Tidal/ParseBP.hs#L119) is calling toPat on the children of TPat_CycleChoose.

But it's more, since it also diversifies the randomness (by fudging the timing).