+\b An argument containing an @ sign will be parsed as a Message-ID.
+The angle brackets that usually delimit Message-IDs are optional;
+\cw{nntpid} will strip them off if it sees them, and will not complain
+if it does not. If the angle brackets are present, anything outside
+them will also be discarded.
+
+\b Otherwise, an argument containing whitespace or a colon will be
+parsed as a group name and an article number.
+
+\b Otherwise, two successive arguments will be treated as a group name
+and an article number.
+
+For example, the following invocations should all behave identically.
+(Single quotes are intended to represent POSIX shell quoting, not part
+of the command line as it reaches \cw{nntpid}.)
+
+\c $ nntpid '<foo.bar@baz.quux>' misc.test 1234
+\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+\c $ nntpid 'foo.bar@baz.quux' misc.test:1234
+\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+\c $ nntpid 'wibble <foo.bar@baz.quux> blah' 'misc.test 1234'
+\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+
+If \cw{nntpid} is given no arguments at all, it will read from
+standard input. Every line it reads will be interpreted as described
+above, except that whitespace will also be trimmed from the start and
+end of the line first.
+
+If you provide the \cw{-a} option (see below), none of the above
+applies. Instead, \cw{nntpid} will expect exactly one command-line
+argument, which it will treat as a newsgroup name.