Defines where in the instance the controlled vocabulary which is identified is utilized. A controlled vocabulary may occur either in the content of an element or in an attribute on an element. The usage can either point to a collection of elements using an XPath via the selector element or point to a more specific collection of elements via their identifier using the specificElements element. If the controlled vocabulary occurs in an attribute within the element, the attribute element identifies the specific attribute. When specific elements are specified, an authorized code value may also be provided. If the current value of the element or attribute identified is not in the controlled vocabulary or is not identical to a code value, the authorized code value identifies a valid code value corresponding to the meaning of the content in the element or attribute.