Frame Strata

Frame strata (sometimes called frameStrata) orders each on the screen, affecting how they overlap. These strata divide the z-axis into nine intervals (from back to front):
 * 1) WORLD (see details)
 * 2) BACKGROUND
 * 3) LOW
 * 4) MEDIUM
 * 5) HIGH
 * 6) DIALOG
 * 7) FULLSCREEN
 * 8) FULLSCREEN_DIALOG
 * 9) TOOLTIP

Frame levels further divide each strata into smaller intervals, numbered 0-10000. Higher numbers appear above lower ones, but only if they share the same strata.

Details

 * WORLD is reserved for the world frame and cannot be assigned.
 * Frames further partition the z axis into Layers when drawing a (e.g. Texture or FontString).
 * Every frame defaults to appearing slightly above its parent, sharing the same strata but having one level higher.
 * Set a frame's strata using:
 * Set a frame's level using:
 * to choose any value
 * or to increase frameLevel to one higher than existing frames which were previously in front but within the same frameStrata
 * for the opposite (no equivalent in XML)
 * to make frameLevel the same as the parent frame (instead of normally being one higher)
 * for the opposite (no equivalent in XML)
 * to make frameLevel the same as the parent frame (instead of normally being one higher)