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There is a special blockdata name n='material' that has an extra meaning to declare that represents a material for import/export materials
Note: all materials of a parent container must have the same fields (value nodes), if there are materials with different properties then must create a container by each type (or define all with the same value nodes some of them unused can have state='hidden')
name - Label that will be visualized by the user. It can be translated.
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