Docs: yet more on $domain_data

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index 912d16dcb18d7c6d3244426fad06bf7072630d42..1c9d17866c2b12a6e27e2a190b2e68f9e76828a8 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -8788,6 +8788,13 @@ other statements in the same ACL.
 .cindex "tainted data" "de-tainting"
 The value will be untainted.
 
+.new
+&*Note*&: If the data result of the lookup (as opposed to the key)
+is empty, then this empty value is stored in &$domain_data$&.
+The option to return the key for the lookup, as the value,
+may be what is wanted.
+.wen
+
 
 .next
 Any of the single-key lookup type names may be preceded by