## C.15. Extension Interactions

Extensions modifying the behavior of existing commands should provide additional parameters by using the pNext field of an existing structure, pointing to a new structure defined by the extension, as described in the Valid Usage section. Extension structures defined by multiple extensions affecting the same structure can be chained together in this fashion. Any structure which can be chained in this fashion must begin with the following two members:

VkStructureType        sType;
const void*            pNext;

It is in principle possible for extensions to provide additional parameters through alternate means, such as passing a handle parameter to a structure with a sType defined by the extension, but this approach is discouraged and should not be used.

When chaining multiple extensions to a structure, the implementation will process the chain starting with the base parameter and proceeding through each successive chained structure in turn. Extensions should be defined to accept any order of chaining, and must define their interactions with other extensions such that the results are deterministic. If an extension needs a specific ordering of its extension structure with respect to other extensions in a chain to provide deterministic results, it must define the required ordering and expected behavior as part of its specification.