Supporting Workbook Cache (Cell C2)

The corresponding content from externalLink2.xml is:

<externalLink …>
  <externalBook xmlns:r="http://schemas.openxmlformats.org
    /officeDocument/2006/relationships" r:id="rId1">
    <sheetNames>
      <sheetName val="Sheet1"/>
      <sheetName val="Sheet2"/>
      <sheetName val="Sheet3"/>
    </sheetNames>
    <definedNames>
      <definedName name="NameInExternalWorkbook"
        refersTo="='Sheet1'!$B$1"/>
    </definedNames>
    <sheetDataSet>
      <sheetData sheetId="0">
        <row r="1">
          <cell r="B1">
            <v>2</v>
          </cell>
        </row>
      </sheetData>
      <sheetData sheetId="1"/>
      <sheetData sheetId="2"/>
    </sheetDataSet>
  </externalBook>
</externalLink>

Supporting workbook data caches store the top-level structure of the workbook (sheet names, defined names, cell table). Only the cells referenced are cached. This supporting workbook data cache indicates that the workbook being referenced by C2 has three sheets, whose names are "Sheet1", "Sheet2", and "Sheet3", and has a defined name of "NameInExternalWorkbook". Additionally, the cell table shows that cell B1 in this workbook is the cell being referenced. A copy of the cell table is stored locally, inside the workbook containing the external link.

The @r:id="rId1" on the top level <externalLink> element indicates the @Id of the relationship from the externalLink2.xml part, which indicates the location of the actual external workbook.