att.declaring provides attributes for elements which may be independently associated with a particular declarable element within the header, thus overriding the inherited default for that element. [15.3 Associating Contextual Information with a Text]
Module tei — The TEI Infrastructure
Members ab back body div div1 div2 div3 div4 div5 div6 div7 facsimile floatingText front geo gloss graphic group lg listAnnotation media msDesc object p ptr ref sourceDoc standOff surface surfaceGrp term text u
decls⚓︎ (declarations) identifies one or more declarable elements within the header, which are understood to apply to the element bearing this attribute and its content.
Status Optional
Datatype 1–∞ occurrences of teidata.pointer separated by whitespace

The rules governing the association of declarable elements with individual parts of a TEI text are fully defined in chapter 15.3 Associating Contextual Information with a Text.