Image courtesy of Mike Verta (www.mikeverta.com)
.MXS
The Maxwell Render scene file format. It contains all the geometry in your scene, cameras and their settings, materials and material assignments. Note that it does not contain the actual textures used in materials or any HDR / MXI textures used in your scene.
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Same as the .STLAY file, except it stores the layout of Maxwell Render UI.
Image courtesy of Tom Rusteberg (www.wanderplay.com)