[#3340] Changes after review:

 - prefix IPv6 Lease => IPv6 prefix lease
 - removed extra comma
 - added a note that subnet-id is optional

Author: tomaszmrugalski

doc/sphinx/arm/hooks-lease-cmds.rst

@@ -841,9 +841,10 @@ An example IPv4 lease deletion by ``"hw-address"`` is:
    }
 
 The IPv6 address leases are deleted the same way, but using :isccmd:`lease6-del`. The
-prefix IPv6 leases are also deleted using :isccmd:`lease6-del`, but with some extra
+IPv6 prefix leases are also deleted using :isccmd:`lease6-del`, but with some extra
 steps. The prefix should be referenced by its address and prefix length should be ignored.
-For example, to delete 2001:db8:1::/48, the following command can be used:
+For example, to delete 2001:db8:1::/48, the following command can be used. The
+``subnet-id`` parameter is optional.
 
 ::
 

src/hooks/dhcp/lease_cmds/lease_parser.cc

@@ -231,7 +231,7 @@ Lease6Parser::parse(ConstSrvConfigPtr& cfg,
             prefix_len = getUint8(lease_info, "prefix-len");
         } else {
             isc_throw(BadValue, "Incorrect lease type: " << txt << ", the only "
-                      "supported values are: IA_NA, and IA_PD");
+                      "supported values are: IA_NA and IA_PD");
         }
     }