Let's follow Bootstrap's example:

• Replace AnchorJS with a Hugo render hook twbs/bootstrap#32953

Tasks

• Initial work via:
  • Drop AnchorJS in favor of Hugo markdown render hook #1463
• Followup: Header self-link: improve style, ux, customizability, and reusability #1813
  • Heading self-links: more compact, customizable, and reusable #1831