Is it possible to define custom attributes in Ada? The LRM SEC. 4.1.4(9/4) says:

An attribute_reference denotes a value, an object, a subprogram, or some other kind of program entity. Unless explicitly specified otherwise, for an attribute_reference that denotes a value or an object, if its type is scalar, then its nominal subtype is the base subtype of the type; if its type is tagged, its nominal subtype is the first subtype of the type; otherwise, its nominal subtype is a subtype of the type without any constraint, null_exclusion, or predicate. Similarly, unless explicitly specified otherwise, for an attribute_reference that denotes a function, when its result type is scalar, its result subtype is the base subtype of the type, when its result type is tagged, the result subtype is the first subtype of the type, and when the result type is some other type, the result subtype is a subtype of the type without any constraint, null_exclusion, or predicate.

But this doesn't really tell me the answer. (As a side note, I find this paragraph to be a bit verbose, and at a quick read, a bit difficult to comprehend without a couple re-reads.) If it is indeed possible to do this, how would I do it?