%access.class;
Accessibility Class Elements
Elements added to make it easier to process books and book parts in ways that are more
accessible to people and devices with special needs, for example, the visually handicapped. <alt-text> is a short phrase description of an objects, <long-desc> is a more complete description of the content or intent of an object.
Model
<!ENTITY % access.class "alt-text | long-desc" >