Property :: checkValidity - Check property handle validity

Subordinated property handles might become invalid, when the the instance in the parent handle has changed its type or when reopening the parent handle for any reason. Usually, the situation is automatically handled by validate(), which is called internally in most cases before executing property handle functions.

In this case, however, the application will not notice, that the property handle has changed its access node and other subordinated property handles became invalid.

Calling checkValidity() checks whether reopen the property handle becomes necessary and enables the application to react properly. The function need not to be called, when event handlers have been installed, which react on the DBO_Reopened event.