Implements an existing SVG feature that allows the keywords 'context-fill' and 'context-stroke' when specifying fill and stroke properties: https://svgwg.org/svg2-draft/painting.html#context-paint This only affects SVG sub-trees that are instantiated via a <use> element, and <marker> elements that are instantiated via the 'marker' property on a <path> element. In those circumstances, 'context-fill' and 'context-stroke' are resolved to the value of the 'fill' and 'stroke' properties on the <use> or <path>.