(a) Parties. A party may appear in person or by an officer, partner, or regular employee of the party, or by or with counsel or other duly qualified representative, in any proceeding under the rules in this part. Any party or his or her representative may testify, produce and examine witnesses, and be heard upon brief and at oral argument if oral argument is granted.

(b) Non-parties. One who appears in person before the Commission or a representative thereof, either by compulsion from, or request or permission of the Commission, shall be accorded the right to be accompanied, represented, and advised by counsel.

(c) Special appearance. An appearance may be either general, that is, without reservation, or it may be special, that is, confined to a particular issue or question. A person who desires to appear specially must expressly so state when entering the appearance, and, at that time, shall also state the questions or issues to which the appearance is confined; otherwise the appearance will be considered general. [Rule 21.]