A PTR record, also referred to as a Reverse IP record, is an "A" record in reverse. In the case of an "A" record, DNS lists a Fully Qualified Domain such as www.foo.com and points it to an IP address. A PTR record lists an IP address and points it to a Fully Qualified Domain such as www.foo.com.
Unlike domain names, IP space used by TWC is owned by TWC. TWC assigns the customer the right to use certain blocks of space, which are assigned during the account creation process. The customer may choose DNS service providers, including TWC, a third-party DNS service provider, or the customer may manage their own DNS services. IP addresses, however, may only be managed by the owner of the IP space, which is TWC.
In order to enter PTR records into the TWC DNS server, the IP space must be TWC Commercial owned IP space. This means that it is the IP space is assigned to the customer by TWC for their use only.