<art> element enables associating metadata and a descriptive title with references to images or other media objects. It's primary purpose is to serve as a "managed object" in a re-use or content management context.
Because the base
<image> element doesn't allow
<data> elements in its content there's no direct way to associate classifying or descriptive metadata with
<image> elements. Thus the
<art> element provides a way to do it.
<art> element is for use in block contexts (anywhere
<p> is allowed). The
<art-ph> element is for use in phrase contexts (anywhere
<ph> is allowed).
With DITA 1.3 the
<art> element could be specialized from
<div>, which would remove the need for separate
<art-ph> element types.
<art>is specialized from
+ topic/p d4p-formatting-d/art