Do I need Visa under class-G?

Under Transit (G) category it says

“c. Flight crew-members and foreign passengers are exempted from the requirement should they stay within airports for no longer than 24 hours. Otherwise, transit G should be obtained beforehand.”

In here what does it mean by “within airports”?

Am I correct to assume that if I transfer from PVG to SHA within 4 hours time, holding a Sri Lankan Passport plus a Canadian PR card, I do not need any?

I am travelling in 4 days from now. Thank you very much for any clarification.