Used for kinds of internal referencing, i.e., a cross-reference to another part of the paper
With the exception of <footnote>, this element may be used to reference anything that has an @id or @xml:id attribute (an attribute of type ID). This single element takes the place of the many named types of references (such as figure references, table references, and citation references).
Cross-references to footnotes use <footnoteref> rather than <xref>.
This is an EMPTY element
<emphasis>, <para>, <quote>, <subtitle>, <td>, <term>, <th>, <title>
...
<para>With land claimed in the New World, an expedition was mounted to
establish a settlement. The first expedition failed. Led by Sir Richard
Grenville in April 1585, it encompassed 600 men of which 105 remained in
the colony while Grenville returned to England for additional provisions.
(<emphasis role="ital">See</emphasis> <xref linkend="mul83"></xref>.)
However, when almost a year passed without Grenville’s return, the
remainder of the expeditionary force took advantage of Sir Francis Drake’s
arrival to seek return passage to England.
<footnote xml:id="mul74"><para>It has been argued that the first expedition
was not a failure. Richard Grenville did return to the colony with
additional provisions not long after Drake’s departure, and he ordered
15 men, supposedly supplied for two years, to remain in the colony while
he returned for new settlers. However, it is unknown whether these men
were present to greet the subsequent expedition.</para></footnote>
</para>
...
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