How ubiquity reads ubuntu.seed?

I submitted a bug about ubiquity to skip some step i want.(https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1103263)
But I found there is no any progress. So I decided to do it myself, here is my thinking:
1) Add a line in ubuntu.seed file, just like this: d-i ubuntukylin/skip boolean true
2) ubiquity reads ubuntu.seed file, if ubuntukylin/skip exists and it's value is 'true', then ubiquity should execute my codes to skip the prepare step, timezone step and console-setup step.
Now, the trouble is that i don't know how ubiquity reads ubuntu.seed file and where it reads? If I add the line to ubuntu.seed file, whether the ubiquity can recognize the key word or not? Maybe I add the judgement codes of ubuntukylin/skip in ubiquity program, it would lead to crash.
In a hurry, I need your help urgently. Can you give some suggestions or maybe someone can resolve the bug?
Thanks.