Any offer of proof made in connection with an objection to any ruling of the Board which rejects or excludes proffered oral testimony shall consist of a statement for the record of the substance of the evidence which the party contends would be established by the testimony.
If the excluded evidence is documentary, a copy of the written evidence shall be marked for identification and shall constitute the offer of proof.
The document shall be retained by the Board as part of the record for purposes of an appeal.
D.C. Mun. Regs. tit. 23, r. 23-1712