Specialization rules for attributes

There are certain rules that apply to attribute specializations.

A specialized attribute has the following characteristics:

• It is specialized from @props or @base.
• It can be integrated into a document-type shell either globally, which makes it available on all elements, or it can be assigned to specific elements by using an expansion module.
• It does not have values or value ranges that are more extensive than those of the attribute from which it was specialized.
• Its values must be alphanumeric, space-delimited values.
• In generalized form, the values must conform to the rules for attribute generalization.