The presence of extensibility points within WS-Transfer is called out in Section 2.4 "Considerations on the Use of Extensibility Points". However, there are several places where such extensibility points are redundantly mentioned. These are:

3.1 Get
  [Body]/wst:Get
      This is a REQUIRED element that has no defined child element content. *However, it MAY include child element content as defined by an extension(s).*

  [Body]/wst:GetResponse
    This REQUIRED element MUST have as its first child element, an element that comprises the representation of the resource. *Additional extension elements MAY be included after the element representing the resource.*

3.2 Put
  [Body]/wst:Put 
    This REQUIRED element MUST have as its first child element, an element that comprises the representation of the resource that is to be replaced. *Additional extension elements MAY be included after the element representing the resource.*

  [Body]/wst:PutResponse
    This REQUIRED element, if it contains any child elements, MUST have as its first child element, an element that comprises the representation of the resource that has been updated. *Additional extension elements MAY be included after the element representing the resource.*

3.3 Delete
  [Body]/wst:Delete
    This is a REQUIRED element that has no defined child element content. *However, it MAY include child element content as defined by an extension(s).*

  [Body]/wst:DeleteResponse 
    This REQUIRED element *MAY contain extension elements.*

Proposal: remove all redundant mentions of extensibility.