operator
key of attribute attribute-name (of element-expression)?
The key of attribute operator 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
        the SGML declaration specifies NAMECASE GENERAL YES for the SGML document being
        processed.
      
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.