Custom tstzrange with importance factored in

Hi,

I want to make a custom range (and multirange type) that carries a few useful details.
Looks like I may have to implement the operators, custom functions and my own aggregator.
Where can I find the code SQL code for anything that relates to the tstzrange range type?

Or would you recommend a different approach?
I essentially want to be able to aggregate multiple tstzranges - each range with its own importance. The aggregation
wouldbe like a a join/intersect where ranges with higher importance override the ones with lower importance. 

Thanks!
Rares