key of specified? attributes element-qualifier* @ numeric-expression

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

When key of is applied to attributes, the "@" (item) indexer is required.

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 attribute form is used rather than attributes.