15.10.5 Omitting <xref> elements from footnotes
The way DITA handles footnotes results in footnotes with IDs not getting callouts unless an <xref> element is added to provide the callout. However, the DITA Open Toolkit is inconsistent on this point. The HTML transform wants the <xref> element, but the PDF2 transform does not.
To exclude <xref> elements from footnotes:
; FootnoteXref = Yes (default, comply with spec) or No (indulge bug in
; DITA-OT for pdf2 output using Idiom/RenderX by omitting footnote
