5.5 Miscellaneous Aspects of Schemas

Several additional aspects of schemas don't fit too well into the preceding discussions.

Abstractness

Any element or type can be made "abstract" by adding an

 abstract="true" 

to the "element" or "simpleType" or "complexType" element where the element or type is specified. Thus you cannot directly use the type or element in an instance of XML; rather, you can use it only in the specification of other types or elements. The "abstract" type/element has "false" as its default value.

Annotations

You can insert "annotations" into a schema for human or automated consumption. These annotations use the xs:annotation element and are fairly obvious when they occur.