An Example

<filter> defines a filter......CPSX.
A filter element is referenced via the 'filter' attribute.
......x="<coord.>": the region to which the filter applies.
......y="<coord.>": the region to which the filter applies.
......width="<length>": the region to which the filter applies.
......height="<length>": the region to which the filter applies.
......filterRes="<width> [height]": the dimensions of the intermediate images in pixels.
......filterUnits="{userSpaceOnUse | objectBoundingBox}": the coordinate system for 'x', 'y', 'width', and 'height'.
......primitiveUnits="{userSpaceOnUse | objectBoundingBox}": the coordinate system for the various length values within the filter primitives and for the attributes that define the filter primitive subregion.
......xlink:href="<iri>": another filter that provides the attributes and child elements for inheritance.