Jakub Kicinski [off-list ref] writes:

On Fri, 24 Mar 2023 19:19:00 +0000 Donald Hunter wrote:

quoted

+sub-type
+~~~~~~~~
+
+Attributes can have a ``sub-type`` that is interpreted in a ``type``
+specific way. For example, an attribute with ``type: binary`` can have
+``sub-type: u32`` which says to interpret the binary blob as an array of
+``u32``. Binary types are described in more detail in
+:doc:`genetlink-legacy`.

I think sub-type is only used for arrays? How about:

 Legacy families have special ways of expressing arrays. ``sub-type``
 can be used to define the type of array members in case array members
 are not fully defined as attributes (in a bona fide attribute space).
 For instance a C array of u32 values can be specified with 
 ``type: binary`` and ``sub-type: u32``. Binary types and legacy array
 formats are described in more detail in :doc:`genetlink-legacy`.

I'll use this text verbatim. Thanks.