targetdoc identifier for the document being
When olinks between documents are resolved for HTML output, the stylesheet can compute the relative path between the current document and the target document. The stylesheet needs to know the targetdoc identifiers for both documents, as they appear in the target.database.document database file. This parameter passes to the stylesheet
the targetdoc identifier of the current document, since that
identifier does not appear in the document itself.
This parameter can also be used for print output. If an olink's targetdoc id differs from the current.docid, then the stylesheet can append the target document's title to the generated olink text. That identifies to the reader that the link is to a different document, not the current document. See also olink.doctitle to enable that feature.