What is a spiroketal compound?

I read a medicinal chemistry book about SGLT2 inhibitors. One of them is tofogliflozin. In that book, they refer to it as spiroketal. Is the spiroketal functional group the red part in this picture? What is special about this group (to deserve a unique name)?


[![enter image description here](https://i.stack.imgur.com/zLTqH.png)](https://i.stack.imgur.com/zLTqH.png)




Quoting the entry on [spiroketal](https://www.ebi.ac.uk/chebi/searchId.do?chebiId=72600) from ChEBI:



> 
> A cyclic ketal in which the ketal carbon is the only common atom of
> two rings.
> 
> 
> 


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