The @subjectrefs attribute
The @subjectrefs attribute specifies one or
more keys that are defined by a subject definition in a subject scheme
map. Multiple values are separated by white space.
The @subjectrefs attribute cascades. When specified
on a topic reference, the @subjectrefs attribute
associates the referenced resource with subjects that are defined in
subject scheme maps.
The DITA 2.0 specification does not indicate processing expectations
for the @subjectrefs attribute. The DITA Technical
Committee expects to specify such expectations in the future.