Thanks BB.

I was just wondering b/c I will be studying in China for this coming fall semester. AC fares YYC-PEK are running $1400US while AC fares SEA-PEK are about $650US. I thought that I might book a flight from YYC-SEA thereby travelling YYC-YVR-SEA on ticket one, SEA-YVR-PEK-YVR-SEA on ticket two and then SEA-YVR-YYC on ticket one again. It would probably save me almost $500US. This is nested, I believe, and would not pose a problem.
Let's say, however, that I decided to fly YYC-YVR-SEA and then SEA-YVR-PEK all on the same day. Would AC check me in all the way to PEK. What would happen if my YYC-YVR was delayed first thing in the morning. Would they allow me to not take the flights to SEA and back? It may be likely that no one has had to deal with this, but if anyone would hazard to guess, I would appreciate this.
Also, if I would book these both within a few weeks, before the commencement of travel couldn't AC argue that I was intending to travel from YYC-PEK and therefore I owed them the full shot? Afterall, the SEA-PEK diversion didn't really just come up.