Its hard to tell without knowing where pq comes from.
But at least I can guess, that the huge raw-string is processed alsewhere, and its result will be stored back into pq. After that pq will be ordered by the given keys and returned.
Thats it mostly from a go point of view. I’d guess the real works happen in that external system, which you did not gave any information about. Also I am not sure if we can help here to actually help to dive into the code in the string even if we knew what external system it is, since its obviously not go.