Adding xenoData to standOff as per #2436

Author: jamescummings

P5/Source/Guidelines/en/HD-Header.xml

@@ -2519,7 +2519,11 @@ grouping makes it easy to avoid accidentally flagging non-TEI data as errors
 during validation of the file against a TEI schema. The
 <gi>xenoData</gi> element, which may appear in the TEI header after
 the <gi>fileDesc</gi> but before the optional <gi>revisionDesc</gi>,
-is provided for this purpose.
+is provided for this purpose. Where the use of <gi>xenoData</gi> is primarily
+to store linked data, contextual information, or stand-off annotations 
+that refer to the contents of the TEI file itself,
+then it is also possible to place <gi>xenoData</gi> inside the <gi>standOff</gi> 
+element. 
 <specList>
   <specDesc key="xenoData"/>
 </specList></p>

P5/Source/Specs/xenoData.xml

@@ -11,6 +11,7 @@
     <memberOf key="att.declarable"/>
     <memberOf key="att.typed"/>
     <memberOf key="model.teiHeaderPart"/>
+    <memberOf key="model.standOffPart"/>
   </classes>
   <content>
     <alternate>