doc:  document problems with using xreflabel in XML docs
Reported-by: Peter Eisentraut
Discussion:
Backpatch-through: master
@@ -47,3 +47,7 @@ Guidelines
usually have xreflabels.
- For an external link, use <ulink>, with or without link text.
+
+- xreflabels added to tags prevent the chapter/section for id's from being
+ referenced; only the xreflabel is accessible. Therefore, use xreflabels
+ only when linking is common, and chapter/section information is unneeded.
