Can I partially spend a gift card, and other questions on gift card limitations

Question

I have several questions:
1) Is it possible to only partially spend a gift card, and save the rest for another time?
2) Within what time frame does teh card needs to be spend?
3) Can I buy a gift card in an apple store in China, and then spend it on a UK app store account?
4) iTunes has an app store where gift cards can be redeemed. Can gift cards be redeemed with the Mac App store as well for Mac software purchases?
5) Can the gift card be used for Apple Store purchases?
6) If one gift card's funds is insufficient for a purchase, can the difference be paid with a second gift card?
7) What are the limitations to spending a gift card, is it just the funds, or also a quantity of apps?
Honestly, I would expect Apple to have a support section that clarifies this, but I can't find it by browsing the Apple website.

Answer 1

Thanks guys,
So in addition to your information I found some more data that helps clarify why e.g. China cards cannot be spend in a UK iTunes app store. Not sure I agree, or approve, and quite sure that Apple looses money this way, but it is what it is.
However, I wonder if this is a workaround:
Ok, so I got a UK iTunes account. I read here that it is possible to change country/region for an account. So... if I were to change my country/region to China, and THEN buy an iTunes gift card, can I then spend that using my relocated-to-China account in the iTunes store? And then, what would happen if I then subsequently change back to the UK?