A controlled string (preferably) that defines howdistinctly the boundary between zones is defined, as governed byboth the contrast between adjacent zones and by the width of theboundary. (eg. sharp, gradational)
Database handle for the object. It is of XML type ID, so is constrained to beunique in the XML document within which it occurs. An external identifier for the object inthe form of a URI may be constructed using standard XML and XPointer methods. This is doneby concatenating the URI for the document, a fragment separator, and the value of the idattribute.