19 CFR §141.31

1. (a)Limited or general power of attorney. A power of attorney may be executed for the transaction by an agent or attorney of a specified part or all the Customs business of the principal.
2. (b)[Reserved]
3. (c)Minor agents. A power of attorney to a minor shall not be accepted.
4. (d)Definitions of resident and nonresident. For the purposes of this subpart, “resident” means an individual who resides within, or a partnership one or more of whose partners reside within, the Customs territory of the United States or the Virgin Islands of the United States, or a corporation incorporated in any jurisdiction within the Customs territory of the United States or in the Virgin Islands of the United States. A “nonresident” means an individual, partnership, or corporation not meeting the definition of “resident.”