How to model writable lists?

Basic question is: how to model writable lists? Here some information I took out from the spec

• I read in wd16 / 4.1.13 writable "The writable Facet describes only the ability of clients to modify this Object's value, not the ability of clients to add or remove children of this Object. If a server does not support addition or removal of Object children through writes, it MUST return an appropriate error response (see Section 9 for details)."
• I don't read anything regarding "writable" in section 6.2 Contract List
• I read in 6.8 Lists and Feeds: "Therefore, in order to add child elements to a list which supports client addition of list elements, servers MUST support adding list elements by writing to the list URI with an Object of a type that matches the list's Contract. Servers MUST return the written resource (including any server-assigned href) upon successful completion of the write."

In my understanding of the language 4.1.13 and 6.8 collide somehow, from 4.1.13 I understand that lists either cannot be replaced or can only be completely replaced and from 6.8 I understand that there is a possibility to add / remove children.