The parent class of all OpenXR composition layer nodes.
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Composition layers allow 2D viewports to be displayed inside of the headset by the XR compositor through special projections that retain their quality. This allows for rendering clear text while keeping the layer at a native resolution.
[b]Note:[/b] If the OpenXR runtime doesn't support the given composition layer type, a fallback mesh can be generated with a [ViewportTexture], in order to emulate the composition layer.
Enables a technique called "hole punching", which allows putting the composition layer behind the main projection layer (i.e. setting [member sort_order] to a negative value) while "punching a hole" through everything rendered by Godot so that the layer is still visible.
This can be used to create the illusion that the composition layer exists in the same 3D space as everything rendered by Godot, allowing objects to appear to pass both behind or in front of the composition layer.