X-Ray Climbing is a technique that allows Samus to go Out of Bounds. It is mainly used while getting stuck inside of a door. Any% Glitched is one of the few categories that takes advantage of X-Ray Climbing.
To perform X-Ray Climbing, make sure to pick-up the X-Ray Scope. Get stuck in a door, and crouch. Use the X-Ray Scope, face the other direction and immediately stop scoping. If done right, Samus should now be forced into a standing position which moves her up by 5 pixels.
There are 2 levels of being stuck in a door: Stuck and Deep Stuck.
A stationary sping jump inside the door shell of a rightwards transition is enough to get Stuck inside of a door for X-Ray climbing most rooms. However for leftward door transitions, or if the room geometry requires it (see the any% glitched X-Ray climb,) you need more backwards momentum during the transition. Taking enemy damage or performing a precise shinespark as the transition begins both are ways to get Deep Stuck in doors.