UMLR — Use of decomposition indicator

Fig. 14.8 uses a decomposition indicator (a lying 8) which is not defined in the document. Actually it is already in UML 1.5 (fig. 3-74 on p. 3-141) in the HiddenComposite. There needs to be some formal description of this icon.

Actually in Enterprise Architect this icon is used as commonplace for decomposition of arbitrary elements. This is a very convenient feature and it should be part of the general UML specification.