defs.m4: Document the behaviour of omitting `KV' apodosis/haeresis args.

[exim-config] / defs.m4

diff --git a/defs.m4 b/defs.m4
index 8be119d..8beb3b1 100644 (file)
--- a/defs.m4
+++ b/defs.m4
@@ -169,16 +169,17 @@ m4_define(<:LOOKUP_DOMAIN:>,
                       _LOOKUP_ARGS(<:$2:>, <:$3:>)}} \
             $3:>)
 
-## KV(key, result)
+## KV(key, [result])
 ##
 ## Extract the value of the named KEY in the ${extract ...}-style string in
 ## the current $value (where it may have been left by `LOOKUP-DOMAIN').  The
 ## RESULT is a pair {IF-FOUND}{IF-NOT-FOUND}; the former may use $value to
 ## refer to the value; the latter may be `fail' (not in braces) to force
-## expansion failure.
+## expansion failure.  The default is to expand to the extracted value or
+## nothing.
 m4_define(<:KV:>, <:${extract {$1}{$value}$2}:>)
 
-## DOMKV(key, result)
+## DOMKV(key, [result])
 ##
 ## Extract the value of the named KEY in the ${extract ...}-style string in
 ## $domain_data; see `KV'.