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a {  mask: url(add.png) add, url(substract.png);}
a {  mask: url(intersect.png) intersect, url(exclude.png);}
a {  mask: url(image.png) intersect, url(image.png) add, url(image.png);}
a {  mask-composite: add;}
a {  mask-composite:;}
a {  mask-composite: add, subtract, exclude;}