Text Encoding Initiative documents are notoriously heterogeneous in structure, since the Guidelines are intended to permit the encoding on any type of text, from tax receipts written on papyrus to Shakespeare plays or novels. Citation Structures are a new feature in the TEI Guidelines that provide a way for documents to declare their own internal structure along with a way to resolve citations conforming to that structure. This feature will allow systems ike the Distributed Text Services (DTS) API, which process heterogeneous TEI documents to handle tasks like automated table of contents generation, the extraction of structural metadata, and the resolution of citations without prior knowledge of document structure.