markerUnits

This value specifies that the markerWidth and markerHeight attributes and the contents of the <marker> element represent values in the current user coordinate system in place for the graphic object referencing the marker (i.e., the user coordinate system for the element referencing the <marker> element via a marker, marker-start, marker-mid, or marker-end property).

This value specifies that the markerWidth and markerHeight attributes and the contents of the <marker> element represent values in a coordinate system which has a single unit equal the size in user units of the current stroke width (see the stroke-width attribute) in place for the graphic object referencing the marker.