Idea for extended OpenRaster layers

openraster-extended-layer-idea.xml

<?xml version='1.0' encoding='UTF-8'?>
<image h="100" version="0.0.4+extendedlayerideas.001" w="100">
  <stack isolation="auto" name="" visibility="visible">
    <layer composite-op="svg:src-over" name="silly eyebrows" opacity="0.333" src="data/layer-00.png" visibility="visible" x="0" y="0">
      <annotation href="data/layer-00-strokemap.dat" media-type="application/x.mypaint-strokemap-v2"/>
      <!--
        An annotation is supplementary data which can be used to describe
        the pixels of the rendered layer (and by inference any source files).
        Annotations are 2d metadata, and MUST NOT be used for rendering a new @src.
        In MyPaint's case, the strokemap data maps pixels to brushstroke settings.
        Boxes or pushpins annotating pixels in a human-readable form are another possibility.
        Annotations SHOULD be preserved (saved) by editors if present when the
        layer was loaded.
        Annotations SHOULD be discarded when a layer is cleared.
      -->
    </layer>
    <layer composite-op="svg:src-over" name="sleeping tiger" opacity="1.0" src="data/layer-01.png" visibility="visible" x="0" y="0">
      <source href="data/tiger.pdf" media-type="application/pdf"/>
      <!--
        A source data file contains the source data for the rendered layer.
        There may be more than one source file, e.g. HTML with images, or LaTeX+bibtex (!)
        The rendered pixel data is placed in @src, and must be kept up to date
        when its sources change.
        The intent is to allow display programs to use the @src directly,
        and to allow editors which can't render the layer's sources to show whatever the
        originating editor rendered.
        Editors which can't re-render these files SHOULD discourage the user from interfering
        with the pixel data in the layer's @src file, and MUST discard all sources if the
        layer @src is "unlocked for editing" in some way or painted over.
      -->
      <metadata href="data/tiger-COPYING" media-type="text/plain"/>
      <!--
        A metadata file describes the rendered pixels as a whole,
        and by inference any source files.
        It is the one-dimensional counterpart to annotation.
        More than one metadata file is permitted.
        Typical uses: license info.
        Metadata files SHOULD be preserved by editors if present when the
        layer was loaded.
        Metadata SHOULD be discarded when a layer is cleared.
      -->
    </layer>
    <layer composite-op="svg:src-over" name="background" opacity="1.0" src="data/background.png" visibility="visible" x="0" y="0">
      <source href="data/background-tile.png" media-type="application/x.mypaint-background-tile"/>
    </layer>
  </stack>
</image>