OVERRIDABLE enables a read-only property of a definition, inherited from the diagram, to be changed (or written to) when the definition is initially created, despite the fact that it is read-only. OVERRIDABLE is only used at the diagram level to specify that a property belonging to a definition representing a symbol drawn on that diagram, can be changed when the symbol is initially created, even though it is read-only.

The keyword is used in the Diagram specification, not the XML Element definition specification.

In the following example, the XML Element definition inherits its value for the “XML Schema” property from the XML Element symbol it is defining, which in turn inherits the value of its “XML Schema” property from the diagram it is placed on. When you initially put the XML Element symbol down on the diagram workspace, you can change the value of the “XML Schema” property of the XML Element definition. After you click OK to close the definition, then reopen it, you will notice that the “XML Schema” property is read-only and can no longer be changed.