Appeals — Certiorari — Discovery orders — Work product privilege — Circuit court did not depart from essential requirements of law in preliminarily overruling objections to discovery seeking party and non-party production of information relating to opinions, observations, credentials, experience, and writings of expert witness who had been listed on defendants’ witness list, but later withdrawn after witness, along with his entire file, had been presented for deposition — Work product privilege was not properly preserved as to certain party production requests where privilege was not asserted below — Claim of work product protection as to properly preserved production requests is not ripe for review where privilege log has not yet been filed — Non-parties — Court notes that, although non-party cannot be compelled to file privilege log, nothing in trial court’s order prevents non-party or counsel from segregating documents claimed to be privileged and requesting evidentiary hearing on that issue