<link> defines an association or hypertextual link among elements or passages, of some type not more precisely specifiable by other elements. 16.1 Links
Module linking — 16 Linking, Segmentation, and Alignment
In addition to global attributes att.pointing (@target, @evaluate) att.typed (@type, @subtype)
targets specifies the identifiers of the elements or passages to be linked or associated.
Status Optional
Datatype 2–∞ occurrences of  

<rng:ref name="data.pointer"/>
data.pointer
separated by whitespace
Values two or more pointers (URIs), separated by whitespace
Note
This attribute is deprecated. It is retained for backward compatibility only; the attribute target should be used for preference. It is an error to supply both attributes, but one or the other must be present.
Used by
linkGrp model.global.meta
May contain Empty element
Declaration 

<rng:element name="link">
 <rng:ref name="att.global.attributes"/>
 <rng:ref name="att.pointing.attributes"/>
 <rng:ref name="att.typed.attributes"/>
 <rng:optional>
  <rng:attribute name="targets">
   <rng:list>
    <rng:ref name="data.pointer"/>
    <rng:ref name="data.pointer"/>
    <rng:zeroOrMore>
     <rng:ref name="data.pointer"/>
    </rng:zeroOrMore>
   </rng:list>
  </rng:attribute>
 </rng:optional>
 <rng:empty/>
</rng:element>
element link
{
   att.global.attributes,
   att.pointing.attributes,
   att.typed.attributes,
   attribute targets { list { data.pointer, data.pointer, data.pointer* } }?,
   empty
}
Schematron

<sch:report test="@target and @targets">You may not supply both
@target and @targets</sch:report>
Schematron

<sch:report test="not(@target) and not(@targets)">You must
supply either @target or @targets</sch:report>
Schematron

<sch:assert test="contains(@target,' ')">You must supply at least two
values for @target</sch:assert>
Example
<s n="1">The state Supreme Court has refused to release <rs xml:id="R1">
  <rs xml:id="R2">Rahway State Prison</rs> inmate</rs>
 <rs xml:id="R3">James Scott</rs> on bail.</s>
<s n="2">
 <rs xml:id="R4">The fighter</rs> is serving 30-40 years for a 1975 armed robbery conviction in <rs xml:id="R5">the penitentiary</rs>.
</s>
<!-- ... -->
<linkGrp type="periphrasis">
 <link targets="#R1 #R3 #R4"/>
 <link targets="#R2 #R5"/>
</linkGrp>
Note
This element should only be used to encode associations not otherwise provided for by more specific elements.
The location of this element within a document has no significance, unless it is included within a linkGrp, in which case it may inherit the value of the type attribute from the value given on the linkGrp.