Original text:
of the CoRE link format RFC6690.  The target of the link MUST be a URI formatted string.  The client MUST indicate the desired content format for publishes to the topic by using the ct (Content Format) <del> link attribute in the link-format payload.  The client MAY indicate the lifetime of the topic by including the Max-Age option in the CREATE request. Topics may be created as sub-topics of other topics.  A client MAY create a topic with a ct (Content Format) link attribute value which describes a supported serialization of the CoRE link format RFC6690 such as application/link-format (ct=40) or its JSON or CBOR serializations.  If a topic is created which describes a link </del>  serialization, that topic may then have sub-topics created under it as shown in create-sub-fig. A topic creator MUST include exactly one content format link attribute value (ct) in the create payload.  If the Broker does not <del> support the indicated format for both publish and subscribe, it MUST reject the operation with an error code of 4.00 "Bad Request". </del>  There is no default content format.  If no ct is specified, the Broker MUST reject the operation with an error code of 4.00 "Bad upon topic creation.  The lifetime of a topic MUST be refreshed upon create operations with a target of an existing topic. <del> Topic hierarchies can be created by creating parent topics.  A parent topic is created with a POST using ct (Content Format) link attribute value which describes a supported serialization of the CoRE link format RFC6690, such as application/link-format (ct=40) or its JSON or CBOR serializations.  If a topic is created which describes a link serialization, that topic may then have sub-topics created under it as shown in create-sub-fig. </del> The CREATE interface is specified as follows: Client -> Broker

Reviewer comments:
removed duplicate description of hierarchy, added a constraint to allow only one topic to be created at a time, added text to allow additional target attributes in links for created topics

Revised text:
of the CoRE link format RFC6690.  The target of the link MUST be a URI formatted string.  The client MUST indicate the desired content format for publishes to the topic by using the ct (Content Format)  <ins> link attribute in the link-format payload.  Additional link target attributes and relation values may be included in the topic specification link whena topic is created. The client MAY indicate the lifetime of the topic by including the Max-Age option in the CREATE request. Topic hierarchies can be created by creating parent topics.  A parent topic is created with a POST using ct (Content Format) link attribute value which describes a supported serialization of the CoRE link format RFC6690, such as application/link-format (ct=40) or its JSON or CBOR serializations.  If a topic is created which describes a link </ins> serialization, that topic may then have sub-topics created under it as shown in create-sub-fig. A topic creator MUST include exactly one content format link attribute value (ct) in the create payload.  If the Broker does not  <ins> support the indicated format for both publish and subscribe, or if there is more than one "ct" value included in the request, the Broker MUST reject the operation with an error code of 4.00 "Bad Request". Only one topic may be created per request.  If there is more than one link included in a CREATE request, the Broker MUST reject the operation with an erroro code of 4.00 "Bad Request". </ins> There is no default content format.  If no ct is specified, the Broker MUST reject the operation with an error code of 4.00 "Bad upon topic creation.  The lifetime of a topic MUST be refreshed upon create operations with a target of an existing topic.  The CREATE interface is specified as follows: Client -> Broker