Dan F clarified the CURLOPT_ENCODING description after his changes to

allow "" to enable all support formats.

docs/libcurl/curl_easy_setopt.3

@@ -335,13 +335,18 @@ prompt function.
 .SH HTTP OPTIONS
 .TP 0.4i
 .B CURLOPT_ENCODING
-Three encodings are supported: \fIidentity\fP, which does nothing,
-\fIdeflate\fP which requests the server to compress its response using the
-zlib algorithm, and \fIgzip\fP which requests the gzip algorithm. This
-is a request, not an order; the server may or may not do it.  This
-option must be set (to any value) or else any unsolicited encoding done
-by the server is ignored. See the special file lib/README.encoding for
-details.
+Sets the contents of the Accept-Encoding: header sent in an HTTP
+request, and enables decoding of a response when a Content-Encoding:
+header is received.  Three encodings are supported: \fIidentity\fP,
+which does nothing, \fIdeflate\fP which requests the server to
+compress its response using the zlib algorithm, and \fIgzip\fP which
+requests the gzip algorithm.  If a zero-length string is set, then an
+Accept-Encoding: header containing all supported encodings is sent.
+
+This is a request, not an order; the server may or may not do it.  This
+option must be set (to any non-NULL value) or else any unsolicited
+encoding done by the server is ignored. See the special file
+lib/README.encoding for details.
 .TP
 .B CURLOPT_FOLLOWLOCATION
 A non-zero parameter tells the library to follow any Location: header that the