2.2.7.2 Supporting Link

Each formula element (section 2.2.2.6) which references external data refers to a XTI (section 2.5.344). The XTI (section 2.5.344) references a SupBook record (section 2.4.271) that specifies the type of supporting link and, in certain cases, specifies additional data about the supporting link.

There are several types of supporting links. The type of the supporting link used is specified by the cch and virtPath fields of the SupBook record (section 2.4.271). Supporting link types are specified in the following table:

Supporting Link Type	Meaning
Self-Referencing	A reference to the current workbook. This supporting link type supports cross-sheet (1) references, where the target sheets (1) are specified by the XTI (section 2.5.344). This record also supports defined name or User Defined Function (UDF) references on the same book.
Same-Sheet Referencing	A reference to the active sheet in the context of the consuming formula (section 2.2.2). This supporting link type is used by formulas in macro sheets and in defined names to reference the sheet (1) of the caller.
Add-in Referencing	A reference to a UDF on any Excel Linked Library (XLL) or COM add-in.
External Workbook Referencing	A reference to an External Workbook (section 2.2.7.3).
DDE Data Source Referencing	A reference to a DDE Data Source (section 2.2.7.6).
OLE Data Source Referencing	A reference to an OLE Data Source (section 2.2.7.8).
Unused	An unused supporting link. A reference to this type of supporting link can be specified by an XTI (section 2.5.344), but that XTI (section 2.5.344) MUST NOT be used by any external reference consumer (section 2.2.7.1).