[Click] How does AddressInfo work?

[Dagang LI]

Dear all,

I am now trying to create a new element that doesn't stand in the packet 
flows. Its mere function is to mentain a state and manipulate some other 
elements accordingly via handlers. I guess this element can work in a 
similiar way as AddressInfo, since this AddressInfo is not involved in 
the flows either.

I found AddressInfo is used (only?) in the parse functions. Its class 
methods are called only when CLICK_TOOL is not defined. I have no idea 
what this CLICK_TOOL is. Is it just a flag for the makefile? And what is 
the purpose of it? Is there a kind of guideline to follow for these 
elements that don't participate packets manipulation? I also want to 
know if I want to check whether a certain element exists in the router 
configuration, what shall I do?

Any help will be highly appreciated!

Best regards,
Dagang