Writing Plugins - Documentation?

Can anyone point me at some Nutch Plugin documentation which goes into
more detail than

http://wiki.apache.org/nutch/WritingPluginExample-0.9

I want to understand all the different places where you might put a
plugin and why/how you might do so.

Basically I am trying to extra some information out of the pages I am
crawling and want to figure out whether I should put that info into
the lucene indexes or elsewhere...

Alex