Relationship

The corresponding content from sheet1.xml.rels is:

<Relationships …>
  <Relationship Id="rId1" Type="http://…/hyperlink"
    Target="http://www.w3.org/" TargetMode="External"/>
</Relationships>

This hyperlink points external to the workbook (@TargetMode="External"), and the URL is found in the value of @Target to be "http://www.w3.org/".