Since version 3.4.5 SVG vector graphics can be used as masks for views. Please note, that the SVG mask can currently only contain one path, that will be used as a mask. To add a mask open the view you want in the product builder. Above the Canvas, click the "Edit mask" button:
A menu will open. To add a mask, click on the image icon beside the text "Image URL".
In this example the used SVG is a simple circle. Every transparent area of your SVG is masked, only the rest is displayed - this applies to all content you have added or that the customer adds within that view.
Additional options in the mask menu allow scaling and positioning of the masking image.