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To add a group of attributes, or in other words, to add a group of variation possibilities (colors, capacity, material, etc.), click on "Add attributes group", fill out the form that appears, and save.
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If you would like to make this the default combination (attribute + product), check the box labeled "make the default combination for this product".
Finally, click on "Add this Combination" in order to save it. It will appear in the attributes list.
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