minimal URL documentation

src/vmod_blobcode.vcc

@@ -155,7 +155,12 @@ byte. For example::
 URL*
 ----
 
-*TODO*
+The ``URL`` decoding replaces any ``%<2-hex-digits>`` substrings with
+the binary value of the hexadecimal number after the % sign.
+
+The ``URLLC`` and ``URLUC`` encodings implement "percent encoding" as per
+RFC3986, the hexadecimal characters A-F being output in lower- and
+uppercase, respectively.
 
 $Function BLOB decode(ENUM {IDENTITY, BASE64, BASE64URL, BASE64URLNOPAD,
                             HEX, URL} decoding="IDENTITY", STRING_LIST encoded)