50 CFR §18.88

1. (a)The presiding officer may:
   1. (1)Require the cross-examiner to outline the intended scope of the examination; and
   2. (2)Exclude cross-examination questions that are immaterial, irrelevant or unduly repetitious.
2. (b)Any party shall be given an opportunity to appear, either in person or through an authorized counsel or representative, to cross-examine witnesses. Before cross-examining a witness, the party or counsel shall state his name, address and occupation. If counsel cross-examines the witness, counsel shall state for the record the authority to act as counsel. Cross-examiners shall be assumed to be familiar with the direct testimony.
3. (c)Any party or party's counsel who fails to appear at the hearing to cross-examine an “adverse” witness shall be deemed to have waived the right to cross-examine that witness.
4. (d)Scientific, technical or commercial publications may only be utilized for the limited purposes of impeaching witnesses under cross-examination unless previously submitted and introduced in accordance with these regulations.