"<marker>"

Creates a marker element that can be used to define graphical objects that can be used repeatedly in a drawing, such as arrowheads or other markers on paths.

• DOM object: SVGMarkerElement
• SVG2 spec: https://www.w3.org/TR/SVG2/painting.html#MarkerElement

<marker id="arrow" refX="3" refY="3" markerWidth="6" markerHeight="6" orient="auto">
  <path d="M 0 0 L 6 3 L 0 6 z" fill="red" />
</marker>

Attribute	Default	Description
viewBox	(none)	A list of four numbers (min-x, min-y, width, height) separated by whitespace and/or a comma, that specify a rectangle in userspace that should be mapped to the SVG viewport bounds established by the marker.
preserveAspectRatio	xMidYMid meet	How to scale the viewport to fit the content. Only applies is viewBox is specified.
markerWidth	3	Width of the marker viewport.
markerHeight	3	Height of the marker viewport.
refX	0	X coordinate for the reference point of the marker, where the marker is centered.
refY	0	Y coordinate for the reference point of the marker, where the marker is centered.
orient	0	Orientation of the marker relative to the path. Supported values: auto, auto-start-reverse, or an angle for a fixed rotation such as 45deg or 3.14rad.