A scrolling page navigation with an animated SVG marker that highlights the currently visible sections. As the user scrolls, a JavaScript routine calculates the vertical position of each linked section relative to the viewport and dynamically updates a smooth path drawn on a transparent SVG overlay. The path traces the indented table-of-contents links, connecting and highlighting all headings that are on screen at once, with rounded line caps and joints. The code uses `getTotalLength` to measure and animate the path along the outline of the active nav items, creating a continuous progress indicator that responds to scroll position and indent changes.