+
+A @code{value-mod} can specify special modifications to a @code{value}:
+
+@itemize @bullet
+@item
+The @code{footnote-number}, if present, specifies a footnote that the
+@code{value} references. The footnote's marker is shown appended to
+the main text of the @code{value}, as a superscript.
+
+@item
+The @code{subscript}, if present, specifies a string to append to the
+main text of the @code{value}, as a subscript. The subscript text is
+normally a brief indicator, e.g.@: @samp{a} or @samp{a,b}, with its
+meaning indicated by the table caption. In this usage, subscripts are
+similar to footnotes; one apparent difference is that a @code{value}
+can only reference one footnote but a subscript can list more than one
+letter.
+
+@item
+The @code{format}, if present, is a format string for substitutions
+using the syntax explained previously. It appears to be an
+English-language version of the localized format string in the
+@code{value} in which the @code{format} is nested.
+
+@item
+The @code{style}, if present, changes the style for this individual
+@code{value}.
+@end itemize