Attribute aliases can be defined by the repeat over action and the using prefix even when the name of the attribute is known. The attribute alias serves to simplify attribute identification when more than one opened element has an attribute with the same name.
An attribute alias can be defined for any form of repeat over or using. Within such a context, the attribute alias-name takes precedence over an element attribute or data attribute with the same name: use of the alias-name refers to the attribute associated with the alias, and not with the attribute whose "real" name is the alias name, if any.
Note that while attribute names themselves are case sensitive in XML and may or may not be case sensitive in SGML, depending on the NAMECASE GENERAL declaration in the SGML declaration, attribute aliases are OmniMark names and as such are always case insensitive.
The only time an attribute alias is required is when either repeat over or using is used with attributes, specified attributes, data-attributes, or specified data-attributes. In these cases, an alias is required so that the selected attribute or attributes can be identified within repeat over or using.
When the operator key of is applied to the selected or iterated item inside using attributes or repeat over attributes, it returns the real name of the attribute, and not the alias name.