diff --git a/author/topics/sections/bibliography.adoc b/author/topics/sections/bibliography.adoc
index 1d4044d1..91ff0246 100644
--- a/author/topics/sections/bibliography.adoc
+++ b/author/topics/sections/bibliography.adoc
@@ -808,6 +808,7 @@ fetched from Relaton
 * If the span information presents information absent in the fetched record, it is added to the record.
 * If the span information presents information corresponding in the fetched record, it overwrites it
 * Information is broken down by type: if an identifier, or URI, or date is of a given type, it overwrites only identifiers of the same type in the fetched record (e.g. `span:docid.BSI[BSI EN 8000]`, `span:date.published[2010]`). The same applies to contributors: contributors of a given type overwrite only contributors of the same type in the fetched record.
+  * For document identifiers, you will need the type of the SDO issuing the document, which is typically the standard organisation abbreviation. Look at the Semantic XML of the document for the currently fetched document, to make sure.
 * Information is replaced, not additive. For example, if there are multiple authors in the fetched record, they are replaced by the listing of multiple authors in the bibliographic spans.
 
 To illustrate, the following citation