Physical operators in SQL Server execution plans: what are rebinds, rewinds and number of executions?

Question

I'm trying to understand physical operators in SQL Server execution plans. This page is quite helpful:

http://technet.microsoft.com/en-us/library/ms191158.aspx

SSMS 2008 shows some physical operator properties that are not displayed in SSMS 2005: Estimated Number of Executions and Number of Executions. But what do these actually mean, and how are they related to rebinds and rewinds?

Estimated Number of Executions is particularly interesting because it doesn't seem to be stored in the XML. So how is it calculated? It seems to be equal to Estimated Rebinds + Estimated Rewinds + 1.0. But if that is the case why is Number of Executions not equal to Actual Rebinds + Actual Rewinds + 1?

Thanks.