The type of element for which this element type can substitute for.
Enable the element described by this IUXmlAttribute to appear anywhere the substituteForTypeName element can appear in a UXML document. For example, if an element restricts its children to <Button> elements (using the uxmlChildElementsDescription property), elements having their substituteForTypeName returning Button will be accepted as children of that element.
The value of this property is used for the element substitutionGroup attribute in UXML schema definition.