When you want to add a footnote, you typically just insert the <fn> element and enter the footnote text. When you insert a footnote, in the output, the footnote marker with the number appears in the text and the footnote appears at the bottom of the page. However, in an HTML output, you can also link to the footnote from another element in the same topic by inserting a cross-references to the footnote element.
Note:
Links to footnotes are only supported in HTML outputs. Use footnotes sparingly, only when they are really needed.