What is the filter primitive subregion of SourceGraphic?

Hello,

I am working on implementing <feTile>, and I’ve run up against something that seems unspecified in the 1.1 spec. Per http://www.w3.org/TR/SVG11/filters.html#feTileElement, “typically the input image has been defined with its own filter primitive subregion…”. What is supposed to happen when the input does NOT have a defined filter primitive subregion, as seems to be the case when the input is SourceGraphic? In other words, what should be the result of this?

<svg version="1.1" baseProfile="basic" preserveAspectRatio="xMidYMid meet" zoomAndPan="magnify" id="svg-root"
  width="100%" height="100%" viewBox="0 0 480 360"
  xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
  <defs>
    <filter id="tile" filterUnits="userSpaceOnUse" primitiveUnits="userSpaceOnUse" x="10" y="10" width="460" height="340">
      <feTile />
    </filter>
  </defs>
  <g filter="url(#tile)">
    <rect x="5" y="5" width="50" height="50" fill="red" />
    <rect x="15" y="15" width="30" height="30" fill="green" />
    <rect x="5" y="5" width="70" height="70" fill="none" stroke="black" />
  </g>
  <rect x="1" y="1" width="478" height="358" fill="none" stroke="blue" />
</svg>

Chrome, IE, Edge, and Inkscape all render this document differently. Note that the <feTile> element is the only element in the filter chain, so it receives SourceGraphic as its input by default. Since there is no previous filter primitive to establish a sub-region, what portion of the <g> element should be tiled?

Ryan

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