mask
If the value is a URI value, the element pointed to by the URI is used as an SVG mask.
If the value is a URI value, the element pointed to by the URI is used as an SVG mask.
MDN
If the value is a URI value, the element pointed to by the URI is used as an SVG mask.
If the value is a URI value, the element pointed to by the URI is used as an SVG mask.
MDN