xorg.conf, vital items

After fighting with screen resolution for two weeks, I wonder which items in xorg.conf are decoration and which ones are being processed. "Identifier" vs "DefaultDepth" ?

I know there is a link covering that question, but I'm unable to recover same.
Yes, I understand that. However as I'm stuck with a low screen resolution and error reports in xrandr, I was trying to improve my situation. And although my initial question may be naive, I still presume that entries like "Vendor" are of no significance.

After having rummaged through umpteen posts and tried countless variations of xorg.conf and xrandr things are the same as a fortnight ago. Still I endeavor to get along without swamping the forum with dmesg and other endless reports.