Footnotes

Capture footnotes for an article in a <fn> element.

The <fn> element must contain an @id attribute containing the unique identifier for the footnote and a child <label> element containing the label for the footnote.
Note: The @id attribute and label element are optional when the <fn> is a child of <table-wrap-foot> and not linked from within the table.
Note: Place the <fn> element directly after the first <xref> element that links to the footnote.

Example

<fn id="cqgac8863fn14">
  <label>15</label>
  <p>Note however that in phase space, the Boyer–Lindquist
time-frequency-dependent spheroidal harmonics form a natural choice of
angular modes, since they are involved in the separability of the wave
equation after taking a Fourier transform in time.</p>
</fn>