The Tor Browser / file revision

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      http://creativecommons.org/publicdomain/zero/1.0/

 -->

 <svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">

   <title>Testcase for alpha mask</title>

   <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=793617 -->

   <mask id="m" maskContentUnits="objectBoundingBox" style="mask-type: alpha">

     <rect x=".1" y=".1" width=".8" height=".8" fill="black" fill-opacity="0.5"/>

   </mask>

   <rect width="100" height="100" fill="blue" mask="url(#m)"/>

 </svg>