ID unique to this type of element?

[Robert William Vesterman]

Is there a way to specify an attribute as being sort of like an ID,
except that it has to be unique to this type of element rather than
unique within the document?

Or, more pleasantly, unique within the parent element's children?

Or, especially pleasantly, unique within the parent element's children
of the same element type?

Thanks,

Bob Vesterman.

 

[Martin Honnen]

Is there a way to specify an attribute as being sort of like an ID,
except that it has to be unique to this type of element rather than
unique within the document?

Or, more pleasantly, unique within the parent element's children?

Or, especially pleasantly, unique within the parent element's children
of the same element type?

A DTD doesn't allow that but a W3C XML schema does:
http://www.w3.org/TR/xmlschema-0/#specifyingUniqueness