Understanding behavior of mosaic compiler_params passed to pl.pallas_call

[ji8er]

In the reduction example in pallas documentation here, I am seeing the same behavior, irrespective of whether I pass

compiler_params=dict(
          mosaic=dict(dimension_semantics=("parallel",))
      )

or

compiler_params=dict(
          mosaic=dict(dimension_semantics=("arbitrary",))
      )

in pl.pallas_call.

Why is this the case? I would have expected some error to be thrown when dimension_semantics was specified as parallel.

Is the dimension semantics more of a hint rather than a constraint ?