key of data-attribute of (attribute-reference)

An operation that returns the "true" name of the attribute. This is most useful when retrieving the real name of an attribute that is being referenced through an alias. The name is uppercased when namecase general yes applies to the SGML document.

Because attributes are always considered part of a shelf of attributes, it always makes sense to ask for the "key" of an attribute, even if the data-attribute form is used rather than data-attributes.