File:SVG double arrow with marker-start and marker-end.svg - Wikimedia Commons
SVG.js v3.0 | Other Elements
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Nadieh Bremer on Twitter: "Brilliant! Draw an arrowhead in the center of an SVG path by using textPath and a unicode ▶️ character: Only a few lines of code & works no
Chapter 14, Marking the Way: Using SVG with CSS3 and HTML5 — Supplementary Material