X-ray as the name says is a tool that makes selected blocks transparent letting you see what you want. You can use it to find needed materials, check out whats wrong with your redstone circuit and more.
The mod comes with 3 funtions:
You can change the hotkeys in the Controls menu(Yes, the games one).
You can change the blocks you want to show/hide in the menu(ctrl+x).
Forge merged files are compatible with the recommended forge release.
(Optional) Download and install NoVoidFog mod which deletes fog deep undergound.
Or Damn That Done Button. A simple mod which changes the position of the “Done” button in the controls menu. After instaling it, that damn button goes to the center bottom of the screen.