Docs: more detail on lookup keys

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index ed5b06a2dc2bd3a28c9fe2b2b3aa18fe75f76733..36ed7ca092f0b8074fba1f652c4bdfacf6614002 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -6755,6 +6755,9 @@ domains = ${lookup{$sender_host_address}lsearch{/some/file}}
 domains = lsearch;/some/file
 .endd
 The first uses a string expansion, the result of which must be a domain list.
+.new
+The key for an expansion-style lookup must be given explicitly.
+.wen
 No strings have been specified for a successful or a failing lookup; the
 defaults in this case are the looked-up data and an empty string, respectively.
 The expansion takes place before the string is processed as a list, and the
@@ -6779,6 +6782,12 @@ domain2:
 Any data that follows the keys is not relevant when checking that the domain
 matches the list item.
 
+.new
+The key for a list-style lookup is implicit, from the lookup context, if
+the lookup is a single-key type (see below).
+For query-style lookup types the key must be given explicitly.
+.wen
+
 It is possible, though no doubt confusing, to use both kinds of lookup at once.
 Consider a file containing lines like this:
 .code