Newbie: how do I find all nodes that have changed?

[Chris]

I'm building a crawler that needs to find all the documents in a 
repository. Once I do the first crawl, how do I go back later and get 
all the documents that have changed?

I could do a full recrawl, but I was hoping there was a faster way to 
find the nodes that had been inserted/updated/deleted since the last crawl.