Stores the symbol (such as an asterisk, numeral, or section mark) that was displayed in the original document to identify a specific footnote, if this symbol is to be preserved
For example, it might be useful to store the symbol to disambiguate mistagged cases in which an author has stated “see footnote b” or “see footnote 14” in the text, but the “see” note has not been tagged as an <xref> element. When the cross-reference has not been tagged, the normal ID/IDREF connection between footnote and reference is missing, and the only connection between the two is the visually matching symbols (“b” and “14”, respectively).