principal place of business
(1) Certain business use Subsection (a) shall not apply to any item to the extent such item is allocable to a portion of the dwelling unit which is exclusively used on a regular basis— (A) as the principal place of business for any trade or business of the taxpayer, (B) as a place of business which is used by patients, clients, or customers in meeting or dealing with the taxpayer in the normal course of his trade or business, or (C) in the case of a separate structure which is not attached to the dwelling unit, in connection with the taxpayer’s trade or business. In the case of an employee, the preceding sentence shall apply only if the exclusive use referred to in the preceding sentence is for the convenience of his employer. For purposes of subparagraph (A), the term “principal place of business” includes a place of business which is used by the taxpayer for the administrative or management activities of any trade or business of the taxpayer if there is no other fixed location of such trade or business where the taxpayer conducts substantial administrative or management activities of such trade or business.
26 USC § 280A(c)(1)
None identified, default scope is assumed to be the parent (part IX) of this section.