Clarify named-rrchecker input format

diff --git a/bin/tools/named-rrchecker.rst b/bin/tools/named-rrchecker.rst
index 28da236b726829b41dc438e08e22087d1a6ea705..470f28fdd4b62e8d825712158770068817e88f70 100644 (file)
--- a/bin/tools/named-rrchecker.rst
+++ b/bin/tools/named-rrchecker.rst
@@ -26,15 +26,24 @@ Synopsis
 Description
 ~~~~~~~~~~~
 
-:program:`named-rrchecker` reads a individual DNS resource record from standard
+:program:`named-rrchecker` reads a single DNS resource record (RR) from standard
 input and checks whether it is syntactically correct.
 
-Options
-~~~~~~~
+The input format is a minimal subset of the DNS zone file format. The entire input must be:
+  CLASS TYPE RDATA
+
+* Input must not start with an owner (domain) name
+* The `CLASS` field is mandatory (typically ``IN``).
+* The `TTL` field **must not** be present.
+* RDATA format is specific to each RRTYPE.
+* Leading and trailing whitespace in each field is ignored.
 
-.. option:: -h
+Format details can be found in :rfc:`1035#section-5.1` under ``<rr>``
+specification. :rfc:`3597` format is also accepted in any of the input fields.
 
-   This option prints out the help menu.
+
+Options
+~~~~~~~
 
 .. option:: -o origin
 
@@ -59,4 +68,4 @@ Options
 See Also
 ~~~~~~~~
 
-:rfc:`1034`, :rfc:`1035`, :iscman:`named(8) <named>`.
+:rfc:`1034`, :rfc:`1035`, :rfc:`3957`, :iscman:`named(8) <named>`.