Conditional GETs

[Ricardo Newbery]

I assume Varnish supports ETags and conditional GETs "If-Modified- 
Since" (IMS) and "If-None-Match" (INM)?

I'm interested in the heuristic applied.

Are IMS/INM requests relayed to the backend before the content is  
served out of cache?

Are distinct copies of each ETagged page saved in cache or are  
previous versions retained unless purged?  Is it possible to purge a  
single ETagged variant or does the entire set need to be purged?

Do the Cache-Control headers moderating conditional requests ("must- 
revalidate",  "proxy-revalidate", and "no-cache") modify this heuristic?

Ric