D.C. Mun. Regs. tit. 23, r. 23-1701
The parties to a show cause hearing shall be the following:
The parties to a protest hearing shall be the applicant and the protestants and their designated representatives, if any.
The parties to a fact-finding hearing shall be the licensee, permittee, or applicant for a license, and such other persons whose appearance the Board deems necessary and who are designated by the Board as parties.
The Board may, in its discretion, permit interested persons other than parties, as defined in this chapter, to intervene in a proceeding for such general or limited purpose as the Board may specify.
A person permitted to intervene under this section shall comply with all conditions fixed by the Board and shall not be considered a party to the proceedings.
At any proceeding before the Board on an application for issuance or renewal of a license, or transfer of a license to a new person or location, the Board shall hear as witnesses all persons residing within and without the neighborhood who desire to be heard; provided that such testimony is not irrelevant or duly repetitious.
D.C. Mun. Regs. tit. 23, r. 23-1701