- refX/refY currently only support double in the SVG2 spec however they should support this:
Source: https://www.w3.org/TR/SVG2/painting.html#MarkerElementRefXAttribute
- markerWidth/markerHeight also currently support double, but are this in the spec:
Source: https://www.w3.org/TR/SVG2/painting.html#MarkerWidthAttribute