Can I install xcode 8.3 without updating my Mac's OS i.e. "OS X El Capitan" (Version 10.11.6)
I was not able to find any reference on Apple's site, However, this link says I can't.
Right now, I've Xcode 8.2.1 installed.
No, the latest version of Xcode (Version 8.3) requires macOS Sierra 10.12. I found this information on the App Store page under the compatibility section on the left side.